Barrons Publishing Dictionary of Computer and Internet Terms 10th

scuzzy [sic] see SCSI.

SD card see SECURE DIGITAL CARD.

SDK

1.Software Development Kit (any of several products).

2.Servlet Development Kit. A software 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

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 gen- eral-purpose sorting algorithms. The program in Figure 233 implements selection sort in Java.

class selectionsort

{

/* This Java program performs a selection sort */

/* Array to be sorted and number of items in it. */ static int a[]={29,18,7,56,64,33,128,70,78,81,12,5}; static int n=12;

public static void main(String args[])

{

/* Perform the selection sort */ for (int i=0; i<=n-1; i++)

{

int m=i;

for (int j=(i+1); j<=n-1; j++)

{

if (a[j]<a[m]) { m=j; }

}

int y=a[m]; a[m]=a[i]; a[i]=y;

}

/* Display the results */ for (int i=0; i<=n-1; i++)

{

System.out.println(a[i]);

}

}

}

FIGURE 233. Selection sort

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; DRAW PROGRAM; 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.

FIGURE 234. Send to front; send to back

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 method of transmitting data one bit at a time over a single wire. See

BAUD; RS-232; SERIAL PORT. Contrast PARALLEL.

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.

FIGURE 235. Serial port

(note “10101” symbol indicating a stream of bits)

433 servlet

series connection of two electronic components so that current flows through one and then the other (see Figure 236). 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 (Figure 237). 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.

FIGURE 237. Serif (highlighted on two letters)

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

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. A Shell 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. A free Shockwave player is available for users to download from www.macromedia.com.