Dictionary of Computer and Internet Terms: S

S

(on a digital camera) shutter-priority autoexposure, the mode in which the user sets the shutter speed (exposure time) and the camera chooses the lens opening (f-ratio); same as TV. See F-RATIO. Contrast A; AV; P; TV.

Sad Mac

(pre OS X only) the icon of a frowning Macintosh computer that announces the Mac has found a hardware problem and cannot finish booting.

Safari

Apple Computer’s web browser for the Macintosh OS and Windows. The free download is available at www.apple.com/safari/download. Compare FIREFOX; INTERNET EXPLORER; OPERA.

safe mode

a way of running Windows with many special hardware drivers disabled, to work around problems with improperly installed hardware or software. Safe mode is used only for testing and to recover from an improper shutdown.

Samba

a widely used, free, open-source software package for linking UNIX systems to Windows file and printer sharing, and for achieving various other kinds of interoperability between networks. For details, see www.samba.org. The name is derived from SMB (Server Message Block), an important part of the protocol that Samba follows. See CIFS; PROTOCOL.

sampling rate

the number of times per second that sound waves are sampled and digitized. The highest frequency that can be reproduced is half the sampling rate. High-fidelity audio is usually sampled at 44.1 kHz (44,100 samples per second) in order to reproduce frequencies up to 22.05 kHz, just above the limit of human hearing. Speech can be stored more compactly by sampling at a lower rate, 22.05 or 11.025 kHz. Another parameter is the number of bits of data stored in each sample. High-fidelity audio requires 16 bits per sample; speech can be reproduced adequately with 8 bits. One minute of sound, sampled at 44.1 kHz with 16 bits per sample, requires about 5 megabytes of disk space (10 megabytes for stereo). See also MP3."

SAN

see STORAGE AREA NETWORK.

sandbox

a safe environment to play in; a protective mechanism that prevents a program from accessing or changing memory or disk space outside of its own permitted area. This is a security feature preventing programs from damaging the system they run on. For example, a Java applet loaded from the World Wide Web runs in a sandbox where it is prohibited access to the hard disk on the browser’s computer.

sans-serif

a typeface that does not have serifs, such as this one. Serifs are small perpendicular marks at the ends of the strokes (sans is French for “without”). Contrast SERIF. See also TYPEFACE.

SAP

a large developer of e-business software, headquartered in Walldorf, Germany. The name stands for the German words for “Systems, Applications, Products.” See www.sap.com.

SATA (serial ATA)

a newer hardware implementation of the ATA hard disk interface, using serial data transmission through a narrow 7-pin connector, giving greater speed than PATA. SATA disk drives also have a new, narrow 15-pin power connector instead of the traditional 4-pin one. See ATA. Compare ESATA; PATA.

saturation

the intensity of a color. A highly saturated color is vivid and brilliant color; to dull a color (decrease its saturation), you add small amounts of its COMPLEMENT, making it closer to gray. See COLOR; HSB.

save

to transfer information from the computer’s memory to a storage device such as a disk drive. Saving data is vital because the contents of the computer’s memory are lost when power is turned off. The opposite process is known as loading, retrieving, or opening.

Save As...

1. to o save a document or drawing under a different name. The first time you save an untitled work, you will use “Save As . . . ” instead of “Save.”
2. to save a file in a different format (e.g., to save a CorelDraw file as a Windows Metafile). See also EXPORT.

SBC

see SINGLE-BOARD COMPUTER.

scalable

able to be used on a large or small scale without major changes. For example, much of the appeal of the UNIX operating system is its scalability; it can be used on small or large computers with little change in the way it works.

scalable font

a font that can be used to print characters of any size. Most printers include scalable fonts; also, TrueType, OpenType, and Type 1 fonts are scalable. The shapes of the characters in a scalable font are stored in the form of vector graphics rather than bitmaps. See FONT; VECTOR GRAPHICS.

scalar

a quantity represented by a single number, as opposed to an ARRAY or LIST.

scalar processor

a computer that operates on only one piece of data at a time. Most computers are scalar processors. Contrast VECTOR PROCESSOR. See also SUPERSCALAR PROCESSOR.

scale

to change the size of a graphical object without changing its shape. Contrast STRETCH. SAP 422423 scattergraph, scatter plot

ScanAlert

a company that developed technology that could be used to verify that a web site has protection from hackers, and providing Hacker Safe certificates to web pages that passed the tests. However, it still is difficult to verify that a web page is truly safe. In 2008 ScanAlert was acquired by McAfee (web address: www.mcafee.com).

scanner

1. a device that enables a computer to read a printed or handwritten page. The simplest scanners give the contents of the page to the computer as a graphic image—a handy way of putting pictures into the computer (see DESKTOP PUBLISHING). There are many nuances involved in scanning artwork. In some ways, it is quite similar to photography and if you are comfortable with a camera, it will make the transition to working with a scanner very smooth. Scanners can adjust the contrast and brightness of the image. Controls for setting the highlight and shadow area are usually provided. Color images can be color-corrected at the scanning stage. With appropriate software, scanners can read the letters of typewritten text, transmitting them into the computer as if they were typed on the keyboard (OCR). This process, however, is seldom 100% accurate. You will find it necessary to proofread scanned copy very carefully.
2. Several other kinds of electronic devices are called scanners, including bar code readers (see BAR CODE) and devices for scanning the radio spectrum.

scattergraph, scatter plot

a graph that shows points of data plotted on an x-y coordinate system. Also called an x-y graph. Scattergraph scientific notation see EXPONENTIAL NOTATION.

scissors

1. a tool available in paint programs that allows you to define an area of the picture that you wish to separate from its surroundings. The resulting cutout may be resized (scaled), stretched, rotated, or moved. The scissors tool is one of several SELECTION TOOLS available to you. Others include the LASSO, MAGIC WAND, and box selection tools. To save space, these tools may be grouped together in your toolbox and only one may be visible at a time.
2. icon for “cut the selected item to the Clipboard.” See also COPY; PASTE. FIGURE 229. Scissors icon

SCO

a software company that sued several companies claiming that it owned a copyright to part of the code in the open-source operating system Linux. Its claims were denied (SCO v. Novell).

SCR

1. (silicon controlled rectifier) an electronic component that functions as a latching switch for direct current. Compare TRANSISTOR. Usage note: The hyphenation silicon-controlled rectifier is incorrect. The term means a controlled rectifier made of silicon, not a rectifier controlled by silicon.
2. (as a filename extension) screen saver. In Windows, an .scr file is just like an .exe file except that it can be installed as a screen saver; the assumption is that it will display graphics. A common way to trick people into running a malicious program is to give it the extension .scr, which they won’t recognize, instead of .exe. See EXE FILE; MALWARE

scratch disk, scratch tape

a disk or tape that one can erase and reuse at any time because it does not contain anything that needs to be kept for future use.

screen

1. a computer display; a monitor.
2. a screenful of information.
3. to process a grayscale image for printing by breaking down the various shades of gray into very small dots. See HALFTONE.

screen capture

see SCREEN SHOT.

screen estate

(informal) space on a computer screen, especially when thought of as a limited resource. A program that consumes too much screen estate will be hard to use concurrently with others. Compare REAL ESTATE.

screen saver

a program that automatically blanks the screen of a computer, or displays a moving picture, when the computer has not been used for several minutes. The original purpose of screen savers was to prevent “burn-in” (i.e., to keep the screen coating from wearing out in places where bright parts of the image were constantly displayed). Modern screens are less vulnerable to burn-in, and today, screen savers serve mainly to protect the privacy of users who are away from their desks, and to save energy when used in conjunction with monitors that turn themselves off when the screen goes blank. Screen savers also provide entertainment. See also "GREEN PC; ENERGY STAR.

screen shot, screen snapshot

an image of the current screen, saved as a bitmap.
Snapshots of the screen are easy to obtain: on the Macintosh, hold down Command and Shift, then press 3. This places a bitmapped image of the screen in a PICT file in your root directory. In Windows, pressing the Print Screen key puts a copy of the entire screen onto the CLIPBOARD. Holding down Alt while pressing Print Screen saves a bitmap of the active window only.

script

1. a style of type that resembles cursive handwriting (not italics), as shown in Figure 230.
2. a file containing commands to be executed, such as a SHELL SCRIPT or a script of dialing commands for a communication program. See also JAVASCRIPT; VBSCRIPT; PERL; PYTHON; CGI.
3. a file or printout containing a copy of information that was displayed on the screen.

scroll

1. to move information across the screen as if the screen were a window or porthole through which you are looking. For example, all word processing programs can scroll vertically, and some can also scroll horizontally.
2. (slang) to type gibberish rapidly and repeatedly in order to disrupt a discussion in a chat room. (This makes all the real messages scroll by too fast for people to read them.) See CHAT ROOM.

scroll bar

the bar at the right-hand side and/or bottom of a window that enables you to scroll the window (i.e., look at different areas of the data that the window is displaying), treating the window as a portion of a larger picture. To scroll, click on the arrows at the ends of the scroll bar or use the mouse to move the scroll box along the bar. For an illustration, see WINDOW.

Scroll Lock

a key on the PC keyboard that toggles the keyboard between two modes. Almost all software ignores the difference between the two modes, but in Microsoft Excel, the Scroll Lock key switches between two ways of moving through a spreadsheet. With Scroll Lock turned off, the arrow keys move the cursor from cell to cell, all over the screen; the spreadsheet holds still until the cursor actually moves off the screen. With Scroll Lock on, the cursor always stays in the same place on the screen, and the entire spreadsheet moves beneath it.

SCSI

(Small Computer Systems Interface, pronounced “scuzzy”) a standard way of interfacing a computer to disk drives, tape drives, and other devices that require high-speed data transfer. Up to seven SCSI devices can be linked to a single SCSI port. Thus, a single SCSI adapter can interface a computer to one or more hard disks, a CD-ROM drive, a tape drive, and a scanner.
SCSI is especially popular with Macintoshes and UNIX workstations but is also used on some PC-compatible computers, where it is supported by device drivers. Almost all SCSI hard disks use the same device driver, with no need for further settings to be made; that makes SCSI hard disks easier to install than any other type. Other SCSI devices such as CD-ROM drives require additional device drivers. This is often done in two layers: an ASPI (Advanced SCSI Programming Interface) device driver for the SCSI system, and various drivers that issue ASPI commands to specific devices.
The cable that comes out of a SCSI port is essentially an 8-bit bus (or 16-or 32-bit if it follows the newer SCSI-2 or SCSI-3 standard). The devices connected to it are daisy-chained with a SCSI terminator (a resistor pack) at the end. Each device, including the SCSI port itself, has an address between 0 and 7 inclusive; most addresses are switch-selectable to prevent conflicts. See also BUS; DEVICE DRIVER. Contrast ESDI; IDE.

scuzzy

[sic] see SCSI.

SD card

see SECURE DIGITAL CARD.

SDK

1. Software Development Kit (any of several products).
2. Servlet Development Kit. Asoftware programming package for Java, from Sun Microsystems.

SDRAM

(synchronous dynamic random access memory) a type of RAM chip whose output is synchronized with the system bus, making data available to the CPU more quickly than with FPM or EDO RAM. SDRAM normally communicates with the CPU at a bus speed of 100 to 133 MHz (200 to 266 for DDR SDRAM). Contrast EDO; RDRAM. See also DDR.

SDSL

(Symmetric Digital Subscriber Line) a type of high-speed network connection provided through ordinary telephone lines. Unlike ordinary DSL (ADSL), SDSL is symmetric (that is, the upload and download speeds are the same), but ordinary telephone service is not included. Depending on the local situation, the data rate of SDSL ranges from 160 kbps to 2.3 Mbps. See DSL and cross-references there.

SDTV

standard-definition television; television with a resolution of about 640 × 480 pixels, or 720 × 480 pixels if the pixels are narrower than they are high. This is the resolution of traditional analog TV, although SDTV can be transmitted digitally. Contrast HDTV.

search and replace

to work through a file, changing every occurrence of a particular sequence of characters into some other sequence of characters. In Macintosh software, this is usually called Find and Change. See EDITOR.

search engine

a computer program that searches through large amounts of text or other data. For example, a search engine for the WORLD WIDE WEB can be accessed at www.yahoo.com or at www.google.com. Depending on the search engine, there are generally several ways to search. If you type a phrase such as golden isles, the search engine will normally search for all documents that contain golden and/or isles, giving highest priority to those that contain both words. Alternatively, you can specify that you want only the documents that contain the whole phrase, and you can specify boolean (“and” and “or”) relationships between words you are searching for (e.g., “Visa OR MasterCard” versus “Visa AND MasterCard”). There is generally a help button that explains how to perform various kinds of searches. See also BOOLEAN QUERY; FULL-TEXT SEARCH.
Some people pay large amounts of money to try to get their web sites listed on search engines. This is unnecessary because every search engine’s job is to find all possible web sites by itself, and major search engines gladly accept additional web addresses from anyone who wants to submit them. Search engine operators do not take kindly to attempts to manipulate the system by listing a web site dishonestly to generate more hits (see GOOGLEWHACKING; META TAG). See also ROBOT (definition 3); SPIDER.

seat

1. (noun) a place where a person can use a computer system or software product. The cost of software is often calculated in terms of seats. For example, a multi-user computer that supports five users has five seats; so does a group of five personal computers. See LICENSE; PER SEAT.
2. (verb) to insert an integrated circuit (IC) or a printed circuit board into a socket.

SECAM

(Séquentiel Couleur avec Mémoire) the type of analog color TV signal used in France, now being displaced by digital television. The screen consists of 625 lines, interlaced, and a complete scan takes 1/25 second. Color information is modulated on two subcarriers at 4.406 and 4.250 MHz. Contrast DIGITAL TELEVISION; HDTV; NTSC; PAL.

second-generation computers

computers made with discrete transistors in the 1950s and 1960s.

Second Life

a virtual world created by Linden Research, Inc. Although it is similar in appearance to a game, the designers’ goal is to create a virtual world that can be used for real business. Users can customize avatars and their environment; the majority of the world’s content is created by users. The free client is available at www.secondlife.com.

secondary mouse button

the mouse button used to call up the action menu. For a right-handed user, this is usually the right mouse button. The left mouse button (the PRIMARY MOUSE BUTTON) is used to select objects. Left-handed users have the option of reversing the default order for mouse buttons; they can use the right mouse button as the primary button and the left button as the secondary.

section sign

the symbol § which is used to mark sections of text for reference (usually in legal documents). The section sign can also be used as a footnote symbol. See FOOTNOTE.

sector

part of a track on a disk. For example, the original IBM PC diskette system partitions the diskette into 40 circular tracks with each track having 8 sectors. See DISK; TRACK.

Secure Digital Card

(SD card) a type of flash-memory non-volatile storage card that incorporates a cryptographic security system to prevent copyright violations, often used in digital music players. Compare COMPACTFLASH; FLASH MEMORY CARD; MEMORY STICK; MULTIMEDIACARD; SMARTMEDIA.

seed

1. a number that is used to start a series of seemingly random numbers. If the seed remains the same, a random-number generator will produce the same “random” numbers (in sequence) every time you use it. To get seat 428an unpredictable seed, programs sometimes look at the system clock. In Java, you may enter the seed in the constructor for a random number generator. For example, the statement Random rnumgen=new Random(123); creates a random number generator named rnumgen with seed 123. Each time you run this program, the random numbers generated in statements such as int x=rnumgen.nextInt(); will always come in the same sequence. Use this constructor Random rnumgen=new Random(); to generate a sequence that will be different each time the program is run. See also RANDOM-NUMBER GENERATOR.
2. an original host in a BitTorrent system. See BITTORRENT. seek time the average time taken by a disk drive to seek (move) from one track to another.

segmentation fault

an error in a program causing it to try to access a memory address that does not belong to it.

select

to tell the computer you are ready to work with an object. You can select one or more objects at a time. Usually, you select an object by clicking on it with the mouse. To select a group of objects, use MARQUEE SELECT or hold down the Shift key while clicking on individual objects until they are all included in the bounding box.

selection area

the selected part of an image.

selection marquee

see MARQUEE SELECT.

selection sort

algorithm for sorting the elements of an array by first selecting the lowest-valued item, then the next lowest, and so on. In practice, the lowest-valued item is interchanged with the first item in the part of the array being searched, and the search is confined to the remainder of the array from then on. Selection sort is probably the easiest to remember of the many general-purpose sorting algorithms.

selection tools

(in graphics programs) tools provided to define an area or choose an object to be worked with. Examples include the POINTER, LASSO, MAGIC WAND, and SCISSORS.

selvage

detachable perforated strips on the edges of printer paper.

semiconductor

a material that is neither a good conductor of electricity nor a good insulator, and whose conduction properties can therefore be manipulated easily.
Semiconductor devices, such as diodes, transistors, and integrated circuits, are the essential parts that make it possible to build small, inexpensive electronic machines. The most widely used semiconductor material is silicon. Each atom in a silicon crystal contains four outer-level (or valence) electrons. A pure silicon crystal is not a very good conductor because these electrons normally stay bound to their atoms.
An N-type semiconductor region is formed by adding a bit of impurity to the pure silicon. This process is known as doping. The impurity added is a material such as phosphorus, in which each atom has five valence electrons. The result is a crystal much like the original one, except that there are now a few extra electrons floating around (one for each atom of phosphorus that was added). The whole crystal is called an N-type region because it contains movable negative charges. If an impurity with only three valence electrons, such as boron, is added to the silicon crystal, gaps are left in the crystal structure because there are not enough electrons to fill all the spaces in the crystal. Each gap is called a hole. Even though a hole is nothing but the absence of an electron, it can be thought of as carrying a mobile positive charge. A semiconductor region with an excess of holes is called a P-type semiconductor region.
Electric current can flow in an N-type region in much the same way that it flows in a regular conductor. In a conductor, the current is made up of outer-level valence electrons that are not too tightly bound to their atoms. When a negative voltage is applied to one end of the N-type region and a positive voltage is applied to the other, the loose electrons will be repelled by the negative voltage and attracted by the positive voltage. Current can flow in the P-type region, but the process is quite different. If a negative voltage is applied to one end of the P-type region, the electrons will be repelled. However, the P-type region does not contain any mobile electrons. What an electron can do is jump into one of the holes. This process creates a new hole where the original electron used to be. We can think of the hole itself as moving toward the negative voltage, carrying a positive charge with it.
A semiconductor diode is formed by joining a P-type region and an N-type region. A transistor consists of a thin layer of one type of semiconductor between two layers of the opposite type. A semiconductor integrated circuit is made by placing many P and N regions on a single chip, so as to form a complex circuit containing many miniature transistors and other circuit elements.

send backward; back one

comparable commands that send the selected object down one layer. See also ARRANGE; BRING FORWARD; BRING TO FRONT; DRAWPROGRAM; FORWARD ONE; SEND TO BACK; TO BACK; TO FRONT.

send to back; to back

comparable commands that send the selected object to the bottom layer. See also ARRANGE; BACK ONE; BRING FORWARD; DRAW PROGRAM; FORWARD ONE; SEND BACKWARD; SEND TO FRONT; TO FRONT.

separator pad (separation pad)

in any printer or fax machine that takes loose sheets of paper, a stationary pad across which the paper passes when it is being fed in, to introduce friction and help separate the top sheet of paper from the rest.
The separator pad is commonly two or three inches wide and is placed in the middle of the paper path. It should be cleaned or replaced if the printer tends to pick up more than one sheet at a time.

sequential-access device

a data-storage device in which it is necessary to read through all preceding records before the computer finds the record it is looking for. Tape storage devices are examples of sequential-access devices. Contrast RANDOM-ACCESS DEVICE.

serial-access device

see SEQUENTIAL-ACCESS DEVICE.

serial bus

a system for rapid communication among components of a computer using a minimum number of wires. Successive bits of each byte or word travel along the same wire, rather than along separate wires as in a conventional bus. See BUS. For examples, see FIREWIRE; USB.

serial mouse

a mouse that is attached to a serial port of a computer. See MOUSE.

serial port

a connection by which a computer can transmit data to another device using serial transmission—that is, one bit at a time. Windows PCs typically have two serial ports labeled COM1 and COM2, one of which may be an internal modem; UNIX systems often identify their serial ports as /dev/ttya and /dev/ttyb. Most serial ports follow the EIA-232D (RS-232) standard. See RS-232.

series

connection of two electronic components so that current flows through one and then the other. Contrast PARALLEL. FIGURE 236. Series circuit (two resistors)

serif

the short finishing strokes of the letterforms in a roman typeface, present in I F A and absent in IFA. It is thought that the horizontal nature of serifs helps guide the reader’s eye along the line of type. Contrast SANS-SERIF. See also TYPEFACE.

server

a computer that provides services to another computer (called the client). On multitasking machines, a process that provides services to another process is sometimes called a server. For specific examples, see FILE SERVER; WEB SERVER; X SERVER.

server-side application

a computer program that runs on a network server rather than on the client PC. For instance, Java servlets are server-side applications; when you view a web page that contains a servlet, the computation is done on the server rather than on your PC. Contrast CLIENTSIDE APPLICATION.

service

in Windows, a program that runs continuously, unseen by the user, such as a Web or FTP server, or a program with a more mundane function such as updating the system clock; the equivalent of a UNIX DAEMON.

service bureau

a business that provides services to computer users, such as high-quality color printing, disk format conversions, or the like.

service pack

a set of updates to a software package, delivered together or even delivered with the original software. Usage note: The phrase Windows XP Service Pack 2 can mean either “Service Pack 2 for Windows XP” or “Windows XP with Service Pack 2 included.”

service provider

a company that provides computer or networking services to customers. See also ACCESS PROVIDER; INTERNET. "

servlet

a Java program that runs on a web server. By contrast, an applet is a Java program running on a web browser client.

session

1. a period of time during which a person is using a particular computer service, such as a connection to the Internet.
2. an occasion upon which data is written to a recordable CD-ROM. Multisession CDs have had data written to them more than once.

set

1. the input of a flip-flop that places it into state 1, as opposed to the reset input. See FLIP-FLOP.
2. the command in Windows and UNIX, that stores information in the operating system’s environment area (see ENVIRONMENT).
3. in mathematics, a collection of objects of any kind. For example, {2,4, –425} is a set of numbers, and {{2, 3}, {4, 5}} is a set of sets. See INTERSECTION; SET DIFFERENCE; UNION.
4. a data type in Pascal that consists of a group of values of a specified type.

set difference

the set of elements that belong to one set and not to another. For example, the difference between {a, b, c} and {b, c} is {a}.

SETI@home

a distributed computer system where users sign up to have their computers analyze pieces of data received from radio
telescopes, in a search for extra-terrestrial intelligence (SETI). See setiathome.ssl.berekely.edu.

seven layers

see DATA COMMUNICATION.

SGML (Standard Generalized Markup Language)

a standard set of codes for marking boldface, italics, etc., in ASCII text files, which became the basis for HTML. See HTML; XML.

shadow

1. (or shadows) the darkest area in a digitized photograph. Contrast HIGHLIGHT (definition 2).
2. to automatically and constantly copy the contents of memory or a storage device as a backup.

shadow RAM

random-access memory (RAM) that holds a copy of the ROM BIOS. The copy is made at boot-up for faster access because "RAM is faster than ROM. See BIOS; BOOT; RAM; ROM. "

share

1. (verb) to make a file, folder, or printer available to others through a network.
2. (noun) a folder that is shared on a network.

shareware

software that is copyrighted but can be distributed free of charge to anyone. Users are asked or required to make a payment directly to the author if they use the program regularly. Shareware is sometimes misleadingly described as “free” (see FREE SOFTWARE).

sharpen

a paint program filter that sharpens the focus of a defined area by UNSHARP MASKING. It can improve a slightly blurred image. (Don’t expect miracles—the computer cannot compute information that is not in the original picture!) If overused, the sharpen filter can overemphasize small random specks or film grain because it works by increasing the difference between adjacent pixels. See PIXELATE; PIXELIZE; UNSHARP MASKING. For technical details, see CONVOLUTION.

shell

a program that accepts operating system commands and causes them to be executed. For example, when you type a command such as dir, the command is read by the shell. The Windows shell is called COMMAND PROMPT or MS-DOS PROMPT and is derived from command.com, which was part of DOS. UNIX users have a choice of shells, such as the C shell (csh), the Bourne shell (sh), and the Korn shell (ksh).

shell script

a file of commands to be executed by the SHELL (the command processor of an operating system). Windows .BAT files are shell scripts. In UNIX, a shell script can begin with a line to indicate which of several shells should process it; for example, the line #!/bin/csh identifies a script for the C shell. PERL and other programming language interpreters can be used as shells to execute scripts written in their respective languages.

Shell sort

a variation of the insertion sort algorithm (see INSERTION SORT) invented by D. L. Shell. AShell sort is a series of insertion sorts in which each item, instead of being compared with the items next to it, is compared with items a certain number of elements away. On each pass, this number (the skip count) becomes smaller until it reaches 1; thus, the last pass is an ordinary insertion sort. The earlier passes take care of large moves that would be time-consuming in a pure insertion sort.

Shergold, Craig

a young cancer victim who, in 1989, circulated an appeal for postcards. He no longer wants any postcards, but people wouldn’t stop circulating his appeal, which now haunts the Internet, often with altered names and addresses. For more information, see the Guinness Book of World Records. See also HOAX.

shift register

a REGISTER (definition 1) in which all the bits can be moved one place to the left (or the right) when a particular control signal is pulsed. For example, the register containing 0 0 0 0 1 1 0 1 when shifted left once is 0 0 0 1 1 0 1 0, and when shifted twice is 0 0 1 1 0 1 0 0. For an application, see BINARY MULTIPLICATION.

Shockwave

a file format for presenting audiovisual shows on the Web, designed by Macromedia, Inc., which produces the software that interprets it. Afree Shockwave player is available for users to download from www.macromedia.com.

shoeshine

(slang) to move tape back and forth repeatedly like a shoeshine cloth, often done by tape drives that are experiencing media errors.

shortcut

1. in Windows, an ICON that serves as a LINK to a file or icon elsewhere on the same computer. Shortcuts let you put the same program or file into the menu system in more than one place. In Windows shortcut icons are recognizable by an arrow displayed in the corner, and they are represented by files with the extension .lnk in the directory corresponding to the folder in which they reside. To create a shortcut, find the desired program or folder and right-click it. One of the menu options will be ”Create Shortcut.” Then cut and paste or drag the new shortcut to where you want it (usually your Desktop). Contrast ALIAS (Macintosh).

2. a faster way to access a command without having to pick it from a menu. Shortcuts are often indicated by underlined letters on menus; typing the letter (perhaps while holding down Alt) will take you directly to that menu selection. Some menus also indicate explicit shortcuts (such as Ctrl-S), which you can press at any time, even when that part of the menu is not on the screen.

shrinkwrap

the clear plastic coating that covers the boxes in which commercial software is sold. shrinkwrap license a software license that the purchaser is deemed to accept by opening the package. Obviously, if the license is hidden inside the package, there will be some difficulty enforcing it in court, and many provisions of shrinkwrap licenses have never been tested. See also COMPUTER ETHICS; COMPUTER LAW; EULA; LICENSE.

shrinkwrapped product

a product packaged in SHRINKWRAP; a product that is sold in retail stores, not just through mail order catalogs or through personal contact with a specialist.

side effect

an effect of a program or subprogram other than simply computing its output from its input. For example, this Java method swaps the two values in a two-element array, and also has the side effect of changing the global variable t:
static void swap(int a[]) {
"t=a[0]; "
"a[0]=a[1]; "
"a[1]=t; "
}
Side effects are usually undesirable because they disrupt variables used by other parts of the program. If t were declared local, the side effect would not occur.

SIG

1. a special interest group within various organizations and online services.
2. a SIGNATURE FILE.

sigma

1. the uppercase Greek letter ?, which stands for the sum of all possible values of an expression. For example, is read “the sum of i +1 from i =1 to 3” and stands for (1 + 1) + (2 + 1) + (3 + 1).

2. the lowercase Greek letter ?, which stands for the standard deviation in statistics.

signature an identification

code sent with a message identifying the sender of the message. See DIGITAL SIGNATURE.

signature file

a file automatically appended to outgoing e-mail and Internet postings, giving the sender’s name, e-mail address, and other pertinent information. Many people use their signature file (“sig file”) as a means of artistic expression, containing elaborate displays of ASCII GRAPHICS, poetry, or favorite quotes. See also STATIONERY. Users sometimes embarrass themselves by forgetting what is in their signature file. Inside jokes and funny mottoes can be quite out of place on serious correspondence such as job applications.

silicon

the chemical element (atomic number 14) most often used to make semiconductor devices. Its electrical properties can be changed by adding small amounts of impurities. See INTEGRATED CIRCUIT; SEMICONDUCTOR. "

Silicon Creek

an area in suburban Atlanta, Georgia, extending from Buckhead to the city of Norcross, home to several important computer companies, including American Megatrends (AMI), Peachtree Software, numerous Internet service providers, and formerly Hayes and Quadram, makers of important early PC peripherals. Compare ROUTE 128; SILICON VALLEY. "

Silicon Fen

an area surrounding Cambridge, England, which is home to numerous computer and electronics companies and research labs, including a major Microsoft research facility. Compare ROUTE 128; SILICON VALLEY.

Silicon Glen

an area in Scotland comprising Glasgow, Edinburgh, and other nearby cities, home to numerous computer companies; over 25% of the PCs sold in Europe are reportedly produced there. Compare ROUTE

Silicon Valley

the Santa Clara Valley and surrounding area between San Jose and San Francisco, California, including the cities of Cupertino, Sunnyvale, and Palo Alto. It is the home of numerous semiconductor and computer companies, including Google, Hewlett-Packard, Intel, and Apple, as well as Stanford University. Compare ROUTE 128; SILICON CREEK.

silver gelatin print

see GELATIN SILVER PRINT.

SIMM

(single in-line memory module) a tiny printed circuit board to which several memory chips are attached. It plugs into a slot on a larger printed circuit board and is handled as if it were a single integrated circuit. See also DIMM.

simulation

the process of representing the actions of one system by those of another. Acomputer simulation is a computer program that carries out a step-by-step representation of the actions of something in the real world. For example, a computer model of population growth can simulate the behavior of a real population. A deterministic simulation occurs when the future path of the system is exactly determined by the parameters of the system. A Monte Carlo simulation occurs when probabilities are known and a selection of random numbers is used to guide the system. See also EMULATION.

sin, sine

the trigonometric sine function. If A is an angle in a right triangle, then the sine of A (written as sin A) is given by sin A = The function sin(a) in many programming languages calculates the value of sin A, if A is in radians. For an illustration, see TRIGONOMETRIC FUNCTIONS.

single-board computer

a complete computer that resides on a single printed circuit board, usually a small one. Single-board computers are often built into industrial equipment. See also EMBEDDED SYSTEM.

single-byte font

a font that represents each character with a single byte, as in ASCII, ANSI, or EBCDIC, and is therefore limited to 256 or fewer characters. Contrast DOUBLE-BYTE FONT; UNICODE.

singleton

something that is in a set by itself; the only member of a onemember set.

singleton variable

in Prolog, a variable that occurs only once in a fact or rule. Since all variables are local, a singleton variable does not carry information from one place to another, and it should be replaced by an anonymous variable. See ANONYMOUS VARIABLE; PROLOG.

site license

a software license that allows unlimited copying of a computer program for use by a single organization at a specified site. Asite license is often much cheaper than the purchase of multiple copies. See also SOFTWARE LICENSE.

six sigma

a high standard in statistical quality control. In statistics (sigma) represents the standard deviation. If a production process is operating well, then there will be a very small standard deviation in measured performance. This means that only a small number of parts will be defective, and the defective parts will be a few standard deviations away from the mean. In theory, if only those parts that are more than 6 standard deviations away from the mean are defective, then less than 2 parts per billion would be defective. In practice, the six sigma standard is taken to mean 3.4 defects per million.

size

see SCALE.

skew

to bend a graphical object as shown in Figure 238. When you skew an object, you slide one side of its bounding box to the left or to the right. This will slant it or shift its bottom edge uphill or downhill. Skewing can be done interactively with the mouse, or, for more precision, the degree of skew can be specified in a dialog box.

skin

a set of graphics and/or computer code that changes the appearance of a piece of software (Figure 239). For instance, Windows Media Player can be decorated with skins that change its color scheme, window shape, and overall appearance. In games with three-dimensional graphics, skins are also used to personalize the appearance of characters.

SKU

(stock keeping unit) a numbered warehouse bin or package; more generally, a code to identify a product being sold. SKU numbers are often used to identify merchandise in computerized inventory and POINT-OF-SALE SYSTEMS.

skunk works

(slang) a group of engineers and programmers who are deliberately isolated from their employer in an attempt to foster creativity and boost morale.

Skype

a popular Internet phone service. See VOIP. Web address: www.skype.com.

slash

the character /, as opposed to the backslash \.

Slashdot

a popular web site (www.slashdot.org) that provides technologically oriented news for computer enthusiasts. Most of the news stories are contributed by readers. Rob Malda created Slashdot in 1997. It is now owned by OSDN, a subsidiary of VA Software Corporation. The name was chosen so that “slashdot.org” would be confusing when read aloud (“slash dot dot org”).

slave

1. the dependent unit in a pair of linked machines. Contrast MASTER (definition 1).
2. one of a pair of IDE hard disks or other devices connected to the same IDE cable. Generally, jumpers have to be set on IDE devices to identify them as master and slave. Contrast MASTER (definition 2).

sleep transistor

a transistor that cuts off power to an electronic circuit when it is not needed, enabling it to “sleep” and be turned on again electronically.

slide

a single image in a graphical presentation. The slide can be textual, pictorial, or graphical. Slides can also contain animations, sounds, music, and video. See PRESENTATION GRAPHICS.

slide sorter

an on-screen representation of an entire graphical presentation. The individual slides are shown in rows, very small. It is then easy to reorder the slides, assign special effects and timings to the slides, or select the next slide to work on.

SLIP

(Serial Line Internet Protocol) an adaptation of TCP/IP for DIAL-UP NETWORKING. Compare PPP.

slot

a socket in a microcomputer designed to accept a plug-in circuit board. See CARD.

SLR

(single-lens reflex) a camera that contains a mirror in front of the film or image sensor, so that the viewfinder can use the same lens that will actually take the picture. When a picture is taken, the mirror flips up before the shutter opens. Unlike most other cameras, SLRs normally have interchangeable lenses, and the user can see exactly what the picture will look like with any lens. See also DSLR.

small caps

a specially designed alphabet of capital letters that are approximately two-thirds the cap height of the font, LIKE THIS. Text set in small caps has the same visual texture as normal text but gives the emphasis of setting text in all caps. The cross references in this book are set in small caps. See C/SC; EVEN SMALLS.

Smalltalk

one of the first object-oriented programming languages. It was developed at Xerox Palo Alto Research Center (PARC) in the late 1970s and included a powerful graphical user interface that influenced the design of the Macintosh and Microsoft Windows. See GRAPHICAL USER INTERFACE; OBJECT-ORIENTED PROGRAMMING.

smart card

a portable card containing a microprocessor and memory. Smart cards can carry identification information for the individual, and they can be used for electronic payment systems. See also RFID.

smartboard

an interactive, electronic whiteboard manufactured by SMART Technologies. Often these capture all notes and diagrams written on the board so that students can access them online later.

SmartMedia

a type of flash memory storage device used in Olympus digital cameras and other portable devices. SmartMedia cards are square with one corner cut off, and the connectors are on the surface (Figure 240). Compare COMPACTFLASH; FLASH MEMORY CARD; MEMORY STICK; MULTIMEDIACARD; SECURE DIGITAL CARD. Confusingly, the name SmartMedia (capitalized and spaced various ways) has also been used by a number of web page development companies.

SMB

see CIFS; SAMBA.

smear

a retouching tool available in most PAINT PROGRAMs. The smear paintbrush drags color from one area over another, as if you had run your finger over a chalk picture. The smear paintbrush works with the colors already present in the picture; contrast SMUDGE, which adds random mixed colors to the image.

smiley

an icon or representation of a face that is used to give the reader clues of the writer’s emotional state or intention. In plain text messages, smileys can be made with regular text characters (see EMOTICON.) In more modern message systems, colorful, small graphics are used for the same purpose. Some sets of smileys are very extensive and cover a wide range of expressions; some smileys are animated, and some have sound.

smishing

a fraud similar to PHISHING in which the message arrives as a cell phone text message (SMS message) and the victim is told to go to a web site, which then asks for credit card numbers or similar information or downloads MALWARE. See PHISHING.

smoke test

(slang) to start up a machine or computer program for the first time and “see if smoke comes out” (i.e., see if it fails catastrophically).

smooth node

a point (NODE) that defines the shape of a curve but does not mark a sudden change of direction. (The control points lie on a straight line with the node.) Contrast CUSP NODE.

SMTP

(Simple Mail Transfer Protocol) a protocol used to transfer electronic mail between computers on the Internet and other TCP/IP networks. See IMAP; INTERNET; POP; PROTOCOL.

smudge

a retouching tool available in most PAINT PROGRAMs. The smudge spray can randomly mixes colors in an area. The smudge spray can adds texture to the image; with coarse settings, the effect achieved is rather impressionistic. Contrast SMEAR; SPRAY CAN.

smurfing

the practice of maliciously disrupting a computer by pinging it continuously (i.e., flooding it with test data packets to which it must respond). (Smurf is the name of a program often used to do this.) Also known as PING FLOODING. See DENIAL-OF-SERVICE ATTACK.

snagless

(describing connectors) designed not to catch on other objects when pulled in either direction.

snail mail

(slang) ordinary postal mail, as opposed to E-MAIL.

snap point

(of an object in a draw program) a point that clings to the GRID or user-defined GUIDELINEs. Most objects have multiple snap points; generally speaking, they will be at every node that defines the shape of the object.

snap to grid

a mode in which a drawing program lines up all objects on a (nonprinting) grid. This makes it easy to line up parts of diagrams that are drawn separately, rather like drawing with a pencil on graph paper.

sneakernet

(slang) the practice of transferring files from one computer to another by carrying a diskette across the room.

sniffer

a hardware device or computer program for intercepting data packets as they pass through a network either to test the network or to intercept other people’s confidential data. See FIREWALL.

snowflake

see FRACTAL; KOCH SNOWFLAKE.

SOAP

(Simple Object Access Protocol) a protocol for executing methods (procedures, functions, subroutines) on a remote computer using XML to encode the data and HTTP to perform the data transmission. SOAP can be used by COM, CORBA, and other kinds of distributed applications. See COM; CORBA; HTTP; PROTOCOL; XML.

social networking site

a web site where users can build a personalized community to socialize with. Common features include a customizable profile, the ability to add other users as friends, the ease of sharing pictures, music, text, and links, and built-in chat and mail features. Social networking sites are becoming one of the most popular methods of contacting friends and organizing gatherings.

Social networking sites

are often criticized for the amount of time that they can consume, and many schools and libraries specifically block them. There is concern that advertising is often mixed in with content seamlessly and the term FRIEND has lost much of its original meaning when applied to every acquaintance. There are also numerous privacy concerns, particularly with younger users who may be too eager to share personal information with strangers.

social responsibility

see EICC.

socket

1. an electrical connector into which another connector, with pins, can be inserted.
2. a communication path between two computer programs not necessarily running on the same machine. Sockets are managed by a socket DEVICE DRIVER that establishes network connections as needed; the programs that communicate through sockets need not know anything about how the network functions.

Sockpuppet

a fake online identity created by another user so that the user talks through another mouthpiece while pretending not to (like a literal sock puppet). Sockpuppets often pop up in forums to defend the original person’s arguments or to deliver praise in order to make the user seem more popular.

SODIMM

(Small Outline Dual Inline Memory Module) a smaller type of DIMM commonly used in laptop and notebook computers. See DIMM.

soft brush

(in paint programs) a category of tools that includes paintbrushes, airbrushes or spray cans, smear paintbrushes, and clone tools. All of these tools leave soft edges and have transparent strokes. These tools are sometimes grouped together in the toolbox and have similar dialog boxes for their settings.

soft copy

computer output that is only viewable on the computer screen. Contrast HARD COPY.

soft edge

in a graphical image, a boundary between two areas that is diffuse and somewhat blurred.

soft error

an error or defect on a data storage device that is present only intermittently; an error that goes away when the same operation is tried again. Contrast HARD ERROR.

soft hyphen

a hyphen that is used only when the word falls at the end of a line; sometimes called a DISCRETIONARY HYPHEN. Contrast HARD HYPHEN; REQUIRED HYPHEN.

soft page, soft page break

an invisible control code that indicates where the text will break at the end of a page. Unlike a HARD PAGE, a soft page break is inserted by the program and will move if the amount of text on the page changes. See WRAP.

software programs

that tell a computer what to do. The term contrasts with hardware, which refers to the actual physical machines that make up a computer system. The hardware by itself is of little value without the instructions that tell it what to do.
Software can be classified into system software (see OPERATING SYSTEM) and application software. For examples of common types of application software, see WORD PROCESSING, SPREADSHEET, DATABASE MANAGEMENT. For information on creating software, see PROGRAMMING and PROGRAMMING LANGUAGE.

software engineering

the art and science of designing and constructing software. The computer industry has learned from bitter experience that large programs cannot be constructed as casually as small ones. Some principles of software engineering include the following:

1. Before starting a project, estimate the amount of labor it will require, based on previous experience. Err on the side of caution. Do not reduce an estimate just because a manager or customer wishes it were lower.

2. Allow adequate time for planning. Decide exactly what is needed, and if possible, write some of the documentation for the finished product before starting to write the program.

3. “Freeze” the specifications when planning is complete. Make sure clients and higher management understand that any further changes will delay completion and raise costs. The only exceptions are changes proposed by the programmers in order to simplify implementation and improve performance.

4. Set priorities. Which is more important, finishing on time or implementing the full set of features? Can the product be developed incrementally, as a minimal first version followed by upgrades?

5. Use reliable programming techniques, including STRUCTURED PROGRAMMING and appropriate use of COMMENTs.

6. Insist that programmers remove errors as soon as they are found; do not leave debugging for later. You cannot build the upper stories if the foundation is not solid.

7. Keep programmers’ morale high. Long working hours, although traditional in Silicon Valley, do not increase productivity; few people really work more than eight hours a day no matter how long they are at the office.

8. Do not add personnel to a project that is running late; the time taken to orient the new programmers will delay it further. Instead, find ways to help the current programmers work more efficiently. Shield them from unnecessary meetings, administrative chores, and even telephone calls.

9. Deadline crises are a symptom of incompetent management. A well-managed project gets finished on time without going into “crunch mode.” If a manager does not know how long a project will take, that’s not the employees’ fault. If the time needed cannot be estimated in advance, everyone should realize it rather than relying on wishful thinking. See also COMMENTS; CREEPING FEATURISM; STRUCTURED PROGRAMMING.

software interrupt

see INTERRUPT.

software license

an agreement between the publisher of a computer program and the person who buys a copy of it, allowing the software to be used. Some licenses specify that when you buy a copy of a program, you do not really own the copy but have merely bought the right to use it in certain ways. Normally, the license allows you to make a working copy of the program, which would otherwise be forbidden by copyright law (see COPYRIGHT).
Most licenses allow a single copy of the program to be used on only one machine at a time. It can be copied for backup purposes, and it can be moved from one machine to another, but it cannot be actually in use in two places at once. Thus you are forbidden to load the same program into more than one machine through a network (see LOCAL-AREA NETWORK). However, it is usually permissible for several people to use the same program on a multi-user machine with a single CPU.
A site license allows unlimited copying of a program for use by a single organization at a specified site. A site license is often much cheaper than the purchase of multiple copies. Another alternative for schools and colleges is the use of student editions of software; these are less powerful than the commercial versions and are sold at much lower prices. Many aspects of software licenses have not yet been tested in court. In particular, the license document is sometimes packed where the user cannot see it until after buying and opening the software package. In such cases, it can hardly be described as a valid contract. When dealing with 445 software license unclear or unreasonable licenses, users should make a good-faith effort to obey copyright law and to avoid depriving the publisher of income. See also ACTIVATE (definition 3); EULA; FREE SOFTWARE; SHRINKWRAP LICENSE.

software patent

a patent (a legal grant of exclusive ownership for a limited time to the creator of a work of intellectual property) that protects a computer program. In 1981, the U.S. Supreme Court ruled that software can be patented (Diamond v. Diehr). However, the issue is still controversial. Open source advocates (see www.nosoftwarepatents.com) think software patents impede innovation, since others are not allowed to use the patented software without a license from the patent owner. Patents are not supposed to be applied to ideas, such as mathematical theorems, but it may be difficult to distinguish patentable software code from a nonpatentable mathematical idea.
Others argue that patent protection is essential for software development because the programmers need to earn income from their work. In 2005, the European Parliament rejected a proposal for a common system of software patents in the European Union. The issue is still being debated as this book goes to press.

SOHO

abbreviation for “small office, home office.” (Soho is also the name of districts in London and New York City.)

Solaris

the version of UNIX sold by Sun Microsystems. See SUN WORKSTATIONS.

solder

metal which is melted to join other metals without melting them. Most solder consists mainly of tin. Until recently, the solder in electronic equipment was usually 60% tin and 40% lead, but in order to reduce the amount of poisonous lead in landfills, the electronics industry is switching to tin-antimony and other lead-free solders. See ROHS.

solver

1. a computer program that solves equations that may have variables on either side of the equal sign, such as x = 1 + 1/x. This contrasts with ordinary calculators, spreadsheets, and programming languages, which can evaluate only expressions that consist entirely of known values.
2. an add-on for Microsoft Excel that can solve some kinds of optimization problems. The user specifies a target cell that is to be maximized or minimized; some cells representing variables that can be changed; and some constraints, such as specifying that the values in certain cells must be less than or greater than specific values.

sort

to arrange items in numerical or alphabetical order. Many different algorithms can be used to sort a group of items. If the number of items is small, it is probably best to use an algorithm that can be represented by a short program. If the number of data items is large, then it is more important to use a faster algorithm, even if it is complicated. Some algorithms assume that the data items have been read into the memory of the computer. However, if there is a very large number of items, it will be necessary to use an algorithm that works when the data items are software patent 446stored on an auxiliary storage device. Since sorting is such a common operation, many operating systems include built-in sorting algorithms. For examples of specific sorting algorithms, see BUBBLE SORT; INSERTION SORT; MERGE SORT; QUICKSORT; RADIX SORT; SELECTION SORT; SHELL SORT.

Sound Blaster

a line of popular sound cards for PCs marketed by Creative Labs, Inc., of Milpitas, California. Their web address is www.soundblaster.com.

sound card

a circuit board that can be added to a computer to enable or improve its ability to record and reproduce sound. Most current motherboards now include the function of a sound card, but higher audio quality can be obtained by adding a separate sound card. Sound cards often include other features such as a MIDI musical instrument interface, a controller for a CD-ROM drive, and an audio amplifier that can drive speakers. 

source

1. see SOURCE CODE.
2. a place from which information is copied; the opposite of TARGET.
3. one of the three parts of a field-effect transistor (see FIELD-EFFECT TRANSISTOR).
4. an audio signal.

source code

1. a computer program written in a programming language, such as C or Java, as opposed to the machine-language OBJECT CODE into which the compiler translates it. See COMPILER.
2. the HTML code or other special code that underlies a web page or other presentation. To view a web page as source code means to view the HTML code itself rather than the display that results from it. See HTML.

source program

a program written in a programming language (e.g., Pascal, C, or C++) and fed into a computer. The compiler translates the program into a machine-language object program.

SP1, SP2

abbreviations for Service Pack 1 and Service Pack 2, which denote update packages for various software products.

spaghetti code

(slang) a disorganized computer program using many GO TO statements, as easy to read as a plate of spaghetti. Contrast STRUCTURED PROGRAMMING.

spam

unsolicited and unwelcome advertisements sent to people via e-mail or posted in newsgroups. “Spammers” have discovered that they can reach a large audience at low cost on the Internet by posting the same message to all available newsgroups or e-mailing it to all possible addresses. Spamming is considered seriously unethical for two reasons. First, newsgroups and e-mail would be useless if they routinely contained unwanted material. Second, the cost of transporting e-mail and newsgroup postings is not paid by the sender; it is paid by the recipient’s site and other sites along the way. Thus, it is important not to impose expenses on people by sending them unwanted material. In some places, spamming by e-mail is illegal, and there is a strong movement to prohibit it everywhere. More importantly, almost all Internet service providers (ISPs) flatly prohibit both e-mail and newsgroup spam. The few ISPs that allow spamming are ostracized by other sites, which refuse to accept any data from them. See CAN-SPAM; COMPUTER ETHICS; COMPUTER LAW; NETIQUETTE; ZOMBIE.
Experts advise that you should never reply to spam, even to ask to be taken off the mailing list, because that will merely tell the spammer that he has hit a valid address. It is not clear why spam was named after a processed-meat product made by Hormel, but a Monty Python comedy act may be involved. For Hormel’s response to the situation, see www.spam.com.

spam filter

a piece of software that distinguishes SPAM from ordinary e-mail. Spam filters are used in most major e-mail systems and can also run on an individual’s computer.
The way spam is recognized is kept secret, but it involves analysis of vocabulary, recognition of key phrases, and identification of known spam sites. To try to get around spam filters, spammers misspell the names of products and often include large numbers of irrelevant words. See BAYESIAN SPAM FILTER.

spammer

a person who sends out SPAM. Spammers are viewed with great contempt by the entire Internet community.

SPARC

(Scalable Processor Architecture) a microprocessor developed by Sun Microsystems and used in Sun Sparcstations as well as computers made by other manufacturers. It uses RlSC architecture to achieve very high speed. See RISC; SUN WORKSTATIONS;WORKSTATION.

S/PDIF

(Sony/Philips Digital Interface) a format for hardware and software for transferring digital audio files, used on CD players and other audio devices.

speaker-dependent, speaker-independent

see SPEECH RECOGNITION.

special characters

characters that cannot be typed directly from the keyboard, but require entering a special code or selection through the KeyCaps applet (Macintosh) or the Character Map (Windows). Windows software accesses these special characters in many different ways. If you prefer to keep your hands on the keyboard, you can type special characters by holding down the Alt key and typing a fourdigit code on the numeric keypad. (See the table of standard Windows characters at ANSI.) Macintosh users can type special characters by holding down the Option or Ctrl buttons while typing (here the Option key acts like another Shift key). KeyCaps lets you see which typewriter key corresponds to the desired character. See also ANSI; EXPERT SET; IBM PC; UNICODE.

specular highlight

a bright point of light on a reflective or shiny surface.

speech recognition

the use of computers to recognize spoken words. This is a nontrivial task because the same spoken word does not produce entirely the same sound waves when pronounced by different people or even when pronounced by the same person on more than one occasion. The computer must digitize the sound, transform it to discard unneeded information, and finally try to match it with words stored in a dictionary. Most speech recognition systems are speaker-dependent; they have to be trained to recognize a particular person’s speech and can then distinguish thousands of words (but only the words they were trained on). Speaker-independent speech recognition is less effective. The biggest demand for speech recognition arises in situations in which typing is difficult or impossible, such as equipment for the handicapped, highly portable equipment, and computers that are to be accessed by telephone. It is easier to recognize DISCRETE SPEECH (speech with pauses between words) than CONTINUOUS SPEECH, but discrete speech is slow and awkward. Hesitation noises (“uh,” “um”), coughs, and sneezes are sometimes mistaken for words.

speech synthesis

the generation of human-like speech by computer (by computing the pronunciation of each word, not by playing back recordings). Originally handled by special hardware, speech synthesis is now usually done by means of software running on a personal computer with a sound card. The technology to generate understandable speech has existed since the 1960s, but the speech is not completely natural; the intonation and timing are not perfect, and the voice may be monotonous and robot-like.
Speech synthesis is important in making computers accessible to blind people and delivering computer data by telephone. A speech synthesizer is built into Windows.

spell checker, spelling checker

a program that checks the spelling of every word in a document by looking up each word in its dictionary. Many word processors do this as the words are typed. If the word does not appear in the dictionary, the user is alerted to a possible misspelling, and possible corrections are often suggested. Sometimes the correction will be made automatically, but you need to double-check to make sure that the resulting word is correct.
A spell checker will not recognize unusual proper names or specialized terms, but it will often allow you to create your own personal dic spell checker, spelling checkertionary of specialized words you often use. (Be sure not to put misspelled words into it!) Spell checkers are valuable aids to proofreading, but they cannot catch the substitution of one correctly spelled word for another (such as form for from or to for too). Thus they do not guarantee that a document is free of spelling errors.

spider

a program that explores the World Wide Web; a CRAWLER.

SPIM

a SPAM message sent by instant messaging.

spin button

a dialog box element that allows the user to change numbers rapidly by clicking on the up and down arrows or by typing the desired number directly into the number box.

spindle count

in a disk or file sharing system, the total number of actual disk drives (each with a stack of magnetic disks revolving around a single spindle).

splash screen

a screen display or small window that appears briefly while a program is starting up, displaying its name, trademark, and version information.

spline

a curve that connects a set of points smoothly. Figure 246 shows some examples. For details of computation, see B-SPLINE; BÉZIER SPLINE; CUBIC SPLINE.

sploit

(slang; plural sploitz) an EXPLOIT; a way of breaching the security of a system.

spoofing

the act of impersonating a user or a machine. For example, IP spoofing is the act of attaching a computer to the Internet using an IP ADDRESS assigned to a different computer, thereby intercepting communications intended for the other machine. See PHISHING.

spooling

the process of storing computer output before sending it to the printer. See PRINT SPOOLER.

spot color

the use of a specified color of ink in a printing job. Spot color can be used for emphasis or to add interest to documents. Contrast PROCESS COLOR. These terms apply to mass-production printing with a printing press, not to inkjet or laser printers attached directly to computers.

spray can

a tool found in various paint programs that leaves a circular pattern of the selected color. To use it, you press and hold down the mouse button and drag the mouse. The center of the spray pattern will be solid, but the edges will feather out to the background color. If you need a dense, solid color, move the mouse slowly; if you want a wispy trace of color, move the mouse rapidly. You can change the size of the spray can’s coverage area—usually by changing the brush size. A similar tool is the AIRBRUSH. Generally, a program will have either an airbrush or a spray can tool, but not both.

spread-spectrum

a technique of radio transmission in which the frequency changes many times per second in a predetermined but seemingly random sequence. The receiver knows the sequence and follows the frequency changes. Spread-spectrum transmission overcomes interference because two transmitters will never be on the same frequency for more than a moment. Spread-spectrum transmission also provides privacy because the signal is almost impossible to intercept without knowing the sequence of frequency changes. See WIRELESS COMMUNICATION.

spreadsheet

a table of numbers arranged in rows and columns. Paper spreadsheets were used for business data long before computers were invented. The first computer spreadsheet was VisiCalc, used on the Apple II computer in the late 1970s. Recently the most popular spreadsheets has been Microsoft Excel. Here are some general features of these programs:
1. Data is arranged in rows (labeled with numbers) and columns (labeled with letters). Each location in the spreadsheet is called a cell.
2. The computer will do calculations automatically if you enter formulas. For example, to calculate the revenue from the sale of cereal, enter the formula =B2*C2 in cell D2. (The asterisk * represents multiplication; the initial equal sign indicates this is a formula and not a label. When a formula is entered, the spreadsheet will display the result of the formula, not the formula itself, in that cell. However, moving the cell pointer to a cell will let you see the formula for that cell at the top of the screen, and you can edit it if needed.
3. Aformula in one cell can be copied to other cells. For example, the formula in cell D2 can be copied to cells D3 and D4, which will give the total revenue for the other products: The copy command automatically changes formulas when they are copied to new cells. In the preceding example, when you copy the formula =B2*C2 from cell D2 to cell D3, it will become the formula =B3*C3, and in cell D4 it will become =B4*C4. This is because B2 and C2 in the formula in the original cell (D2) were written in the form of a RELATIVE ADDRESS. See ABSOLUTE ADDRESS to learn how to prevent the cell addresses from being changed by the copy command.
4. A formula can contain built-in functions, such as a command to sum all cells in a range. Entering Excel formula =SUM(D2:D4) into cell D5 will automatically calculate the column total (cells D2, D3, and D4). Many such functions are included with spreadsheet programs.
5. Spreadsheets are especially valuable because the formulas will be automatically recalculated whenever one of the numbers is changed. For example, if later in the month you update your sales figures, the program will automatically recalculate the revenue for each item, and the total revenue. This makes spreadsheets especially useful for “what-if” analysis. You can design a spreadsheet with many variables, and see how the result changes when one or more of those variables are changed.
6. Spreadsheets can automatically create graphs of your data. For example, Figure 248 shows a pie chart giving the fraction of the sales of each item. Graphs can also illustrate how a variable changes with time, or how two variables are related to each other.
7. MACROs can be used to combine a series of keystrokes into one command, and advanced macros are themselves computer programs that can interact with users and process data.
8. Modern spreadsheets have added many features to improve theappearance of the output. For example, some cells can be displayed in boldface type, or a cell can be emphasized with shading.
9. Originally, spreadsheets were two-dimensional, making them analogous to putting all of your work on one giant piece of paper. Later spreadsheets added three-dimensional capability, which is analogous to keeping your work on different pages in a notebook. Also, modern spreadsheets allow different worksheets to be automatically linked together. For example, you can put your monthly sales figures in 12 different worksheets, and then have those linked to a single spreadsheet with year-end summary data. See also EXCEL; LOTUS 1-2-3; MACRO.

sprite

a moving element in a graphical display. Most video games use sprites.

spyware software

that monitors a computer user’s activity without his or her knowledge and reports it to a central location. The purpose of spyware ranges from purportedly benign (enforcing copyrights, displaying targeted advertisements) to very malicious (stealing passwords and credit card numbers).
The most common way to get spyware on your computer is to install it yourself. This happens when you are tricked into installing free software that supposedly does something else, such as improve your computer’s performance or enable access to a web site.
Most spyware runs under Microsoft Windows, which formerly allowed web sites to download and install software on your computer automatically (see ACTIVEX). Current versions of Windows ask for permission before installing software, but it is very important for the user to be alert and not give this permission inappropriately. Above all, do not click on web site buttons that offer to do anything to your computer, such as check it or “optimize” it.
Software tools for detecting and removing spyware can be found at www.safer-networking.org and www.lavasoftusa.com. See also ADWARE; MALWARE; VIRUS.

SQL

(Structured Query Language, formerly Sequel) a standard query language used by many programs that manipulate large databases. Here is an example of an SQL query: SELECT NAME, SALARY FROM TABLE1 WHERE SALARY > 35000 This means “Give me the name and salary from each row in TABLE1 where the salary is more than 35,000.” See QUERY LANGUAGE; RELATIONAL DATABASE.

square brackets

the characters [ ], also called simply brackets. Contrast ANGLE BRACKETS; CURLY BRACKETS; PARENTHESES.

SRAM

(Static Random-Access Memory, pronounced “S-ram”) a type of computer memory that does not require a periodic refresh signal. SRAM is more expensive than DRAM and is rarely used as the main memory of a computer system, but it is often used for caches, video memory, and microcontroller systems. See MEMORY; RAM. Contrast DRAM.

SRC

HTML keyword that indicates the file that serves as the source of an image or multimedia data. For example, see HTML.

SSL (Secure Socket Layer)

an encryption system developed by Netscape based on RSAENCRYPTION. SSL protects the privacy of data exchanged by the web site and the individual user. It is used by web sites whose names begin with https instead of http.

stack

1. a data structure from which items are removed in the reverse order from which they were inserted; also called a pushdown stack or pushdown store.
For example, when a program calls a subroutine, information about how to return to the main program is usually placed on the stack. If the subroutine then calls another subroutine, information about how to return to the first subroutine is placed on the stack. Since this information is retrieved from the stack in the opposite order from which it was placed there, each subroutine returns control to the right place. Stacks are very useful for dealing with one operation nested inside another. To push a data item is to place it on a stack; to pop the stack is to remove an item from it. Contrast QUEUE.

stacking order

the order in which objects are arranged in a drawing program. This order determines which objects overlay others. Commands to reorganize the stacking order (Send to Front, Send to Back, Forward One, Back One) are usually found under an Arrange menu. Compare Z-ORDER.

Standard Generalized Markup Language SGML

a standard set of codes for marking boldface, italics, and so on, in ASCII text files, which became the basis for HTML. See HTML; XML.

standard input, standard output

the input and output streams that a computer program reads and writes when not told to use a file; in CONSOLE MODE, the keyboard and screen.

star

the character * (asterisk).

star dot star

the WILD CARD character sequence *.*, which matches all Windows filenames.

star key

the key on a telephone keypad marked with the symbol *. It is often used to give commands to software at the telephone company (e.g., to disable CALLWAITING).

Start button

a button, labeled “Start. . . ”, that is normally on the screen whenever Windows is running. By clicking on the Start button, you can access application programs and other functions of the computer through the START MENU.
If the Start button is not visible, it’s probably because the TASKBAR at the bottom of the screen has been reduced to minimum width. Just move the mouse pointer to where it ought to be, and it will appear. By dragging the taskbar with the mouse cursor, you can restore it to normal width and make it readable again. You can also display the Start menu at any time by pressing Ctrl-Esc.

Start menu

the menu that is called up by the START BUTTON in the corner of the screen under Microsoft Windows. It leads to all the application software that is installed on the computer. To edit or modify the Start menu, open it with the right mouse button rather than the left button.

startup folder

a FOLDER under the Windows START MENU containing programs that are to be run automatically when Windows starts up or when a user logs on.

starvation

in MULTITASKING, a situation where a task can never finish because it can never get a necessary resource, such as a large block of memory. The operating system should detect such tasks and do its best to allocate the resources that they need. See MULTITASKING.

statement

a single instruction in a computer programming language. One statement may consist of several operations, such as X = Y+Z/W (a division, an addition, and an assignment). See PROGRAMMING LANGUAGE.

static

1. in C and related programming languages, a keyword indicating that a variable continues to exist even when the function that defines it is not in use. That is, a static variable remembers its value from one invocation of the function to the next.

2. in C++ and related programming languages, a keyword indicating that a variable exists, or a method can be called, without creating an object of the class to which it is attached, and if several such objects are created, they will all share one copy of the static item.

3. (describing electricity) standing still; accumulating as a charge rather than flowing in a circuit. Static electricity accumulating on the human body can damage integrated circuits when a person suddenly touches them. To prevent this, be sure to touch the frame of the computer before touching anything inside it, and use anti-static spray on carpets.

4. (describing audio or video) popping or frying sounds or speckled patterns like those caused by discharges of static electricity interfering with radio or television reception. In the digital world, this kind of static usually results from an insufficient data transmission rate, or corrupted data, rather than from static electricity.

static IP address

an IP address that is assigned permanently to a computer. A static IP address is needed for any kind of server that people access through the Internet. Contrast DYNAMIC IP ADDRESS.

static RAM

see SRAM.

stationery

1. paper, envelopes, and so forth on which information is to be printed.
2. a template for e-mail messages including colors and graphics to give
it a distinctive appearance, implemented by using HTML.

statistics program

a software package for performing statistical calculations.
Astatistics program works with lists of numbers instead of single values. It should have built-in commands for calculating the average and standard deviation of the elements of a list, for testing hypotheses about the relationships between variables through methods such as multiple regression, for performing transformations (such as taking the logarithm of each of the elements in a list), and for drawing graphs of the data. Examples of statistics programs include SAS (Statistical Analysis System) and SPSS (Statistical Program for the Social Sciences).

status line

a line of information on the computer screen that indicates the current settings of the software and the current cursor position. The contents of a status line will vary depending on the software used; some programs give different information during the execution of different commands. It is a good idea to get into the habit of noticing what is in the status line. If you do not understand what you see there, take a moment to review the manual.

steganography

the concealment of a small message inside a larger file that appears to consist entirely of something else. For example, an encrypted message might be hidden among some slight variations of color at selected points in a picture. Crucially, a person viewing the picture would not know that a message was concealed in it. Messages can also be hidden in inaudible low-level noise superimposed on digitized music. Steganography goes hand-in-hand with encryption but is not the same thing. Encryption makes a message unreadable by unauthorized persons; steganography hides the very existence of the message. See also CRYPTOGRAPHY; ENCRYPTION.

stochastic random

constantly varying; unpredictable; scattered.

storage area network

a computer network that shares disk space using DISK SHARING rather than FILE SHARING. Contrast NETWORK ATTACHED STORAGE.

store

to place a data item into a memory device.

stored program computer

a computer that can store its own instructions as well as data. All modern computers are of this type. The concept was 457 stored program computeroriginated by Charles Babbage in the 19th century and was developed by John Von Neumann. The ability of a computer to store instructions allows it to perform many tasks without human intervention. The instructions are usually written in a programming language. See COMPUTER.

Storm worm

a WORM virus introduced in 2007 that linked thousands of computers into a ZOMBIE network.

stream

1. audio or video content made available by streaming (definition 1).
2. (noun) in C++, Lisp, and other computer languages, a file or device that can be read or written one character at a time. For example, the screen and keyboard can be treated as streams.
3. (verb) to move tape past a read-write head continuously, rather than making short movements with pauses in between.

streaming

1. delivering audio or video signals in real time, without waiting for a whole file to download before playing it. See REALAUDIO.
2. moving a tape continuously. See STREAM (definition 3).

stretch

to increase or reduce either the vertical or horizontal dimension of an object, thereby changing its overall shape. To use the mouse to stretch a selected object interactively, drag out one of the handles at the midpoints of the BOUNDING BOX. Contrast SCALE, which maintains the height-to-width ratio of the object.

string

(character string) a sequence of characters stored in a computer and treated as a single data item. See STRING OPERATIONS.

striping

the practice of spreading consecutive data blocks across different disk drives (e.g., block 1 on disk 1, block 2 on disk 2, block 3 on disk 1 again, and so on). See RAID.

struct

in C and C#, a data structure consisting of several simpler items grouped together.
A struct is not an OBJECT; that is, a struct cannot have METHODs. Java does not have structs; it uses only classes (object types). C# has both. See also CLASS; OBJECT-ORIENTED PROGRAMMING.

structured programming

a programming technique that emphasizes clear logic, modularity, and avoidance of GO TO statements (which are intrinsically error-prone). One of the most important barriers to the development of better computer software is the limited ability of human beings to understand the programs that they write. Structured programming is a style of programming designed to make programs more comprehensible and programming errors less frequent. Because it is more a popular movement than a precise theory, structured programming can be defined in several ways, but it usually includes the following;
1. Block structure. The statements in the program must be organized into functional groups.
2. Avoidance of jumps (“GO-TO-less programming”). It can be proved mathematically that, if a language has structures equivalent to the (block-structured) IF-THEN and WHILE statements in Pascal, it does not need a GO TO statement. Moreover, GO TO statements are often involved in programming errors; the programmer becomes confused as to the exact conditions under which a particular group of statements will execute. Advocates of structured programming allow GO TO statements only under very restricted circumstances (e.g., to deal with error conditions that completely break out of the logic of a program) or not at all.
3. Modularity. lf a sequence of statements continues uninterrupted for more than about 50 lines, human beings have a hard time understanding it because there is too much information for them to keep track of. As an alternative, programs should be broken up into subroutines, even if some of the subroutines are called only once. Then the main program will read like an outline, and the programmer will never need to understand more than about one page of code at a time. (The programmer must know what the subroutines do, but not how they do it.) This principle is sometimes called information hiding—irrelevant information should be kept out of the programmer’s way. Structured programming was first advocated by E. W. Dijkstra in the early 1970s.

stub

1. a temporary substitute for a part of a computer program that has not yet been written. For instance, if a procedure to read numbers from a file has not yet been written, the programmer might put in a stub that simply gives the same number every time, so that the rest of the program can proceed.
2. a declaration that tells how to call a method or function that is defined elsewhere.

StudlyCaps

(slang) INTERCAPS. See also PASCAL NOTATION.

StuffIt

a data compression program for Macintosh and Windows written by Raymond Lau. Like ZIP and WinZip, StuffIt allows several files to be combined into one. StuffIt can also encode and decode BinHex files. A free StuffIt expander program can be downloaded from www.stuffit.com. See DATA COMPRESSION; ZIP FILE.

style (of type)

a particular kind of type, either plain, boldface, or italic, belonging to a specified font. See FONT; TYPEFACE. FIGURE 252. Styles of Helvetica type

style sheet

a file (in WordPerfect, LATEX, HTML, and other publishing programs) that defines the overall layout and type specifications of a document or web page. See CASCADING STYLE SHEETS; DESKTOP PUBLISHING; GRID SYSTEM.

stylus

1. the pen-like part of a graphics tablet. They may contain sophisticated electronics to improve accuracy and measure the pressure placed on the tablet by the artist.
2. a sharp, pen-like device used for pressing on the touchscreen of a handheld computer or PDA. The stylus contains no electronic parts; any object that has a non-marking point but is not too sharp will do the job.

subdirectory

a disk directory that is stored in another directory. See DIRECTORY.

subnet mask

a bit pattern, usually written as four numbers, that indicates which parts of an IP address belong to the same network. The most common subnet mask is 255.255.255.0, which indicates that the first three numbers of the IP address are the same throughout the network. An alternative on larger networks is 255.255.0.0, which indicates that only the first two numbers are the same. Here 255 means “the number in this position is the same throughout the network” and 0 means “this number varies from computer to computer.” More technically, subnet masks are 32-bit binary numbers which are logically ANDed with an IP address to extract the part that identifies the network.

subroutine

a set of instructions, given a particular name or address, that will be executed when the main program calls for it. In most newer programming languages, subroutines are called FUNCTIONs, PROCEDUREs, or METHODs. See STRUCTURED PROGRAMMING; TOP-DOWN PROGRAMMING

subscript

a number or other indicator used to identify a particular element in an array. In mathematics, subscripts are written below the main line, as in x1 or ak. In most computer languages, however, subscripts are enclosed by square brackets, as in X[1] or A[K]. See ARRAY.

subscripted variable

array variable. See ARRAY.

subwoofer

a speaker that reproduces only very low-frequency sounds, used to supplement the other speakers in an audio system.

suit

(slang) a manager or salesman; a (male) worker in the computer industry who is neither an engineer nor a programmer and is therefore not allowed to dress casually.

suitcase

(Macintosh) a special kind of folder that contains system resources (fonts, sounds, desk accessories). For example, you can manage your fonts by keeping them grouped logically in suitcases. Some prefer to store their fonts in typeface families—others group fonts used for specific projects in separate suitcases.

suite

a set of application software from a single vendor that attempts to span the basic uses of a computer. A suite usually has a word processor, a database, and a spreadsheet. The advantage of using a suite is compatibility; you are assured that all of the programs can accept data from any of the others and incorporate them in their own files. On the downside, the individual programs of a software suite sometimes lack desirable features. If additional software is purchased, it may be difficult to get the programs to work together.

Sun Microsystems, Inc.

(Mountain View, California) the company that developed SPARC microprocessors, SUN WORKSTATIONS, the SOLARIS operating system, and the JAVA programming language. Web address: www.sun.com.

Sun workstations

high-performance desktop computers manufactured by Sun Microsystems of Mountain View, California. Most are marketed as single-user systems, although each can support more than one user. All run Solaris (SunOS), a proprietary version of UNIX based on System Vand incorporating some BSD features.
Sun workstations dominated academic computer networking in the 1990s, before PCs were fully network-capable. During their heyday, most Sun workstations used Sun’s proprietary RISC microprocessor called SPARC. Today, Sun workstations use Intel and AMD microprocessors, and Sun’s product line has shifted toward servers. See BSD; SPARC; UNIX; WORKSTATION.

superclass

a class from which another class in an object-oriented programming language is descended. For example, if your applet program myapplet extends the class Applet, then Applet is the superclass for myapplet.See EXTENDS.

supercomputer

a computer designed to run markedly faster than ordinary mainframe computers, generally by using parallel processing. Examples are the Cray vector processors and the Intel iPSC parallel processor.

superior character

a superscript; small letters and numbers set above the baseline like this. Used mainly in mathematical typesetting. See SUPERSCRIPT. Contrast INFERIOR CHARACTER; SUBSCRIPT.

superscalar processor

a computer that is in between conventional SCALAR PROCESSOR and VECTOR PROCESSOR architectures; it accepts instructions like those of a scalar processor but has some ability to double them up and do more than one thing at once at runtime. The PENTIUM is an example of a superscalar processor.

superscript

a small character written above the baseline, like this. In mathematics, a superscript indicates an exponent, which denotes repeated multiplication. For example, 43 = 4 × 4 × 4.

supertwist

a newer type of liquid crystal display (LCD) that produces higher contrast than earlier types. An LCD works by twisting light waves to change their polarization. Supertwist displays produce more of a change in polarization than their predecessors.

support ticket

See TICKET.

surface mapping

the act of applying a surface (complete with color, pattern, shading, and texture) to a 3D wireframe model. See RENDER.

surfing

(slang) the practice of browsing the WORLD WIDE WEB or other information services, much like a surfer riding one wave and then another. surge protector device that absorbs brief bursts of excessive voltage coming in from the AC power line. These surges are created by lightning or by electric motors switching off.

Surge protectors

do little good unless the power line is properly grounded. Always plug the computer into a properly grounded outlet. If possible, do not plug a laser printer into the same outlet strip or extension cord as the computer, because laser printers draw heavy current intermittently.
Many surge protectors also incorporate RFI protectors to help reduce radio and TV interference emitted by the computer into the power line. (See RFI PROTECTION.) Asurge protector cannot do anything about momentary power failures; for that, you need an uninterruptible power supply. See also POWER LINE PROTECTION; UNINTERRUPTIBLE POWER SUPPLY.

surround sound

a system of sound reproduction where there are speakers in several directions from the listener (Fig. 253). This contrasts with stereophonic sound, with just left and right speakers, and monophonic sound,with just one speaker (or multiple speakers playing the same signal). Several systems have been developed for encoding and decoding surround sound in a two-channel stereo signal, and many computer SOUNDCARDs now have surround-sound output. See 5.1; 6.1; 7.1.

suspend

to stop the CPU and input-output devices of a computer whileleaving the contents of memory in place, so that it can resume where itleft off without rebooting. Unlike a hibernating computer, a suspendedcomputer continues to consume a small amount of battery power. Contrast HIBERNATE.

SVGA (Super VGA)

a video resolution of 800 × 600 pixels. Contrast XGA.

swap file

a file used for swap space. In Windows, the swap file is hidden and does not normally appear in directory listings (see HIDDEN FILE). It can be either permanent, and fixed in size, or temporary, and varying in size. Permanent swap files give faster program execution. Besides the swap file used by the operating system, there are also swap files used by particular applications, such as Adobe PhotoShop. See SWAP SPACE.

swap space

disk space that an operating system or program uses as a substitute for additional memory. See VIRTUAL MEMORY; SWAP FILE.

swash

a capital letter with a decorative flourish. Swashes are best used sparingly.

.swf

(Shockwave file) filename extension used by Macromedia Shockwave. See SHOCKWAVE.

swipe

see TRANSITION EFFECT.

switch

1. in electronics, a device for interrupting or rerouting the flow of electric current.
2. in telecommunications and networking, a device for establishing connections between one location and another, doing the work of a telephone operator. For instance, on a computer network, a switch is a device that temporarily creates high-speed paths between different segments as they are needed. It works like a hub but does not add congestion to cables on which the traffic is not actually needed. See BRIDGE. Compare HUB; ROUTER.
3. in C and its derivatives, a statement for choosing different actions corresponding to different values of a variable. Each section must end with break unless you want execution to continue in the next section. Here is an example in Java:

switch (p)
{
case 1:
"System.out.println(”First place\n”); break; "
case 2:
"System.out.println(”Second place\n”); break; "
case 3:
"System.out.println(”Third place\n”); break; "
default:
"System.out.println(”Something else\n”); "
}

switched line

an ordinary (POTS) telephone line on which you establish connections by dialing; the path actually taken by the signals need not be the same when you call the same number twice on different occasions. Contrast DSL; T1 LINE; T3 LINE.

switching power supply

a power supply that regulates the voltage of direct current by switching it off and on very rapidly and then smoothing out the variations. Most computer power supplies are of this type. The advantages of a switching power supply are that it does not waste energy and does not require a heavy transformer, since the incoming AC is chopped to give a high frequency that can be handled by a smaller, lighter transformer. The disadvantage is that it produces radio-frequency interference. See POWER SUPPLY; RFI PROTECTION.

SWMBO

online abbreviation for “She Who Must Be Obeyed.” Used facetiously to refer to one’s wife in imitation of Rumpole, the eccentric and somewhat henpecked lawyer in stories by John Clifford Mortimer.

SXGA (Super XGA)

a monitor resolution of 1280 × 1024 pixels.

symbol font

a font containing symbols or ornaments rather than a regular alphabet. Also called a pi font or DINGBATS.

symbolic algebra

the manipulation of mathematical symbols (not just their numerical values). For example, we can calculate that (a + b) × (c + d) = ac + ad + bc + bd without knowing the values of a, b, c, or d. Symbolic algebra on computers began with the MACSYMA project at MIT in the 1960s. Today, popular symbolic algebra programs for personal computers include MathCad, Maple, Mathematica, and MATLAB. They greatly simplify the formerly tedious process of deriving and manipulating mathematical formulas.

symbolic debugger

program that lets you step through a compiled program, interrupting it at any point and examining or changing the values of variables.
“Symbolic” means that programmer-assigned names in the program are recognized. A symbolic debugger analyzes the source code and the object code together, so that even though the program has been compiled, you can work with it as if you were editing the source program.

symbolic programming

a kind of programming in which variables can stand for pieces of the program itself (symbolic expressions), not just switched line 466numbers, strings, or other values. Lisp and Prolog are examples of symbolic programming languages. See LISP; PROLOG; SYMBOLIC ALGEBRA.

sync pulse

the part of a video signal that indicates when the electron beam should scan each line. See SYNCHRONIZATION.

synchronization

1. the act of making a video display scan each line at exactly the right time, so that the image is displayed correctly. The input to a monitor consists of SYNC PULSEs as well as red, green, and blue video.
2. the process of keeping two or more disk drives up to date relative to each other, by copying the latest version of each file to each device. This is a practical problem if you work with more than one computer, such as a laptop and a desktop machine. The Briefcase feature of Windows helps users synchronize files.

synchronous

occurring in unison with a separate signal. In synchronous data transmission, there are two signals, data and clock. The clock signal indicates exactly when the data line should be read in order to obtain each successive bit. Contrast ASYNCHRONOUS. syntax the set of rules that specify how the symbols of a language can be put together to form meaningful statements. A syntax error is a place in a program where the syntax rules of the programming language were not followed.

syntax diagram

a diagram showing how to arrange elements of a language. For an example see RAILROAD DIAGRAM.

synthesizer

1. a device or program for generating speech sounds by computer. See SPEECH SYNTHESIS.
2. a device for generating musical sounds by computer, usually from MIDI data. See MIDI.

Sys Req key

the key on IBM mainframe terminals that enables the user to communicate with the communications system itself rather than the application program. The IBM PC AT and all subsequent PCs have a Sys Req key, but little or no software makes use of it.

sysadmin (system administrator)

a person who manages a multiuser computer.

systems programmer

person who writes the programs needed for a computer system to function (as opposed to the programs that do particular kinds of useful computation). Some of the programs that systems programmers write include operating systems, language processors and compilers, and data file management programs. Systems programming requires considerable knowledge of the particular computer system being used. Contrast APPLICATIONS PROGRAMMER.