Barrons Publishing Dictionary of Computer and Internet Terms 10th
.pdf
L1 cache |
276 |
L
L1 cache (level-1 cache) the memory cache that is closest to the CPU or included within it.
L2 cache (level-2 cache) a memory cache outside the CPU. Contrast L1 CACHE.
L33T, L33TSPEAK see LEETSPEAK.
L@@K comical way of writing look (i.e., “look at this”) in online advertisements.
label
1.an identifying name or number attached to a particular statement in a computer program.
2.a block of information recorded on a tape to identify it.
3.an identifying name recorded on a disk and displayed by the dir command in Windows and similar operating systems.
lag the delay in transmitting data over a network. In online video, lag may be experienced as choppy movement or images freezing for several seconds. In online games, lag can cause a significant problem for players who cannot see an attack in time to respond to it.
lambda calculus the use of LAMBDA EXPRESSIONS to define functions.
lambda expression a formula that defines a function, originally using the Greek letter lambda (λ) to mark arguments.
Lambda expressions were introduced into formal logic by Alonzo Church in the 1930s. The key idea is that when a mathematician says, “Let f(x) = x + 2,” this is really a definition of f for any argument, not just x. To make this explicit, one can say, “Let f = (λx) x + 2,” where (λx) indicates that x is not part of the function, but merely stands for an argument value.
In C#, the same lambda expression is written (x) =>x+ 2 and can be used in place of a DELEGATE (function pointer).
LAN see LOCAL-AREA NETWORK.
landscape a way of orienting paper so that it is wider than it is high, like a landscape painting. That is, the paper is positioned sideways compared to the way it would otherwise be used (“portrait orientation”). Laser printers typically offer a choice of portrait or landscape orientation.
FIGURE 148. Landscape vs. portrait orientation
277 |
last known good |
laptop a small, lightweight computer (under 8 pounds) with a flip-up screen. Such a computer is powered by rechargeable batteries and is easily portable. Laptops are especially valuable for people who travel frequently and need to be able to work on a computer while on the road. See also DOCKING STATION; PCMCIA. Because of their portability, laptops need special precautions against theft. See COMPUTER SECURITY. Compare NOTEBOOK.
Usage note: The distinction between “laptop” and “notebook” has become blurred; some vendors call all their portable computers notebooks.
large-scale integration the construction of integrated circuits that contain more than 100 logic gates. See INTEGRATED CIRCUIT.
laser (light amplification by stimulated emission of radiation) an electronic device that produces rays of light that are exactly matched in wavelength and phase. Laser beams can be used to detect microscopically tiny detail (such as the pattern on a CD-ROM) and to concentrate energy in a small, precisely located space (as in a laser printer).
laser printer a computer printer that generates an image by scanning a photoconductive drum with a laser beam and then transferring the image to paper by means of electrostatic toner. Laser printers provide highquality output of text and graphics; they are quiet and run fast. Contrast
DOT-MATRIX PRINTER; INKJET PRINTER. See also CORONA WIRE; DRUM;
FUSER; PICKUP ROLLER; SEPARATOR PAD; TRANSFER ROLLER.
lasso a selection tool commonly found in PAINT PROGRAMs; it looks like a rope lariat, and you use it to define an area that you wish to work with. Crucially, the area need not be rectangular; it can be any shape. After selecting the lasso icon, you drag the mouse freehand around the desired area. Once the area is defined, you can scale, move, rotate, change color, apply filters, or perform any operation that is available.
Because the lasso is a freehand tool, it is dependent upon your skill as a mouse operator. Knowing how difficult it is to draw accurately with a mouse, you may want to see if your paint program has other selection tools (such as a MAGIC WAND) that would suit your needs better. See SELECT.
FIGURE 149. Lasso tool
last known good describing the configuration of a computer the last time it was used successfully, before changes. If you disrupt Microsoft Windows
last mile |
278 |
while installing patches or drivers, you can, in most cases, use the System Restore feature to boot from the last known good configuration.
last mile the connection of individual homes or businesses to a communication network. For examples see DSL; WIMAX.
LATEX (pronounced “la-tekh” or “lay-tekh”; alternatively written LATEX) a typesetting system designed by Leslie Lamport and implemented as a set of macros for Donald Knuth’s TEX (see TEX). There are two versions in wide use, LATEX 2.09 and LATEX 2ε; LATEX 3 is under development.
The key idea of LATEX is to separate the job of the author from that of the publication designer. The author uses commands such as \chapter{...} and \section{...} to mark chapter and section titles, figures, quotations, and the like. (Figure 150 shows an example.) Separately, a file called a style sheet specifies how these things should be printed and keeps them consistent. So, while other word processing programs work like a computerized typewriter, LATEXdoes the job of an expert typist and layout artist. See LOGICAL DESIGN.
LATEX is especially popular for typesetting scientific and mathematical books because the full power of the TEX mathematical typesetting system is available. Many scholarly journals are typeset with LATEX, as are most of the books published by several major publishers. LATEX is also popular with graduate students writing theses and dissertations because it is easy to conform to standard formats—just use your university’s official style sheet.
Implementations of LATEX are available for a wide range of computers. The text of this book is written using LATEX.
Latin the language of the ancient Romans; the Roman alphabet (including j, v, and w, which were added to it in modern times), as opposed to the Greek or Russian alphabet.
launch
1.to advertise and release a new product.
2.to start a computer program, especially in a multitasking operating system.
LCD (Liquid Crystal Display) the type of display used on most digital watches, calculators, and laptop computers, and in flat-panel computer displays.
LCDs use liquid crystals, which are chemicals whose response to polarized light can be controlled by an electric field. A polarizing filter is built into the LCD; through this filter, the liquid crystal compound looks light or dark depending on its electrical state.
lead a metal that forms poisonous compounds and should be kept out of landfills and public water supplies. Lead is found in electronic equipment in lead-acid batteries and formerly in SOLDER. See ROHS.
leader a line of dots that connects one side of the page with another, often used in tables of contents, like .......................... this.
279 |
leading |
\documentclass{article}
\title{An Example} \author{Michael A. Covington} \date{June 27, 2008}
\begin{document}
\maketitle
\section{Overview}
This is a sample of a short paper typed with \LaTeX. Notice the commands I use to get \emph{italics} and \textbf{boldface}. I can also typeset mathematical formulas such as $\sum_{x=1}^{5} A_x$.
Notice that I skip lines between paragraphs in the input. This is the second paragraph.
\section{Another section}
This is the second section. It is very short.
\end{document}
An Example
Michael A. Covington
June 27, 2008
1. Overview
This is a sample of a short paper typed with LATEX. Notice the commands I use to get italics and boldface. I can also typeset math-
ematical formulas such as ∑5x=1 Ax.
Notice that I skip lines between paragraphs in the input. This is the second paragraph.
2. Another section
This is the second section. It is very short.
FIGURE 150. LATEX input and output
leading (pronounced “ledding”) the insertion of extra space between lines of type. On old printing presses, this was originally done by inserting strips of lead between rows of type cast in lead. See TYPEFACE.
These lines
are typeset with extra leading.
In some cases, it is actually beneficial to use negative leading—for instance, when setting type in all caps, it is not necessary to allow space for descenders. Such headlines usually look best with negative leading.
THESE LINES ARE TYPESET
WITH NEGATIVE LEADING.
leak |
280 |
leak an error in a program that makes it fail to release memory or other system resources when it terminates. Thus, the available memory, disk space, or other resources are gradually eaten up until the computer is rebooted. Memory leaks are a common error in Windows programs.
Java and .NET programs avoid this problem because of the garbage collection process, which automatically releases memory locations that are no longer being referenced by the program.
leap year a year in which an extra day, February 29, is added to keep the calendar year in step with the earth’s revolution around the sun. If there were no leap years, the calendar would get out of step with the earth’s motion, so that after many centuries, January 1 would occur in the summer instead of the winter.
The rule for identifying leap years is as follows:
•Years divisible by 400 are always leap years. Thus, 2000 and 2400 are leap years.
•Years divisible by 100, but not by 400, are not leap years. Thus, 1900 and 2100 are not leap years.
•Otherwise, years divisible by 4 are leap years. Thus, 2004, 2008, and so on, are leap years.
Leap years were introduced by Julius Caesar. See GREGORIAN CALENDAR; JULIAN CALENDAR.
learning curve a graph representing mastery of a skill plotted against the time spent on learning it. If something is hard to learn to use, it is sometimes described as having a steep learning curve (although, logically, a steep curve should indicate rapid learning).
The term originated in behaviorist psychology but is now used very imprecisely.
lease the right to use an IP ADDRESS temporarily assigned by DHCP. If a lease runs out while the computer is still connected to the network, DHCP automatically renews it or assigns a new address.
LED (light-emitting diode) a semiconductor device that emits light when an electric current passes through it. The bright red display on some digital clocks is made of LEDs. Other available LED wavelengths are infrared, orange, yellow, green, and blue.
White LEDs consists of a blue-light emitter plus a fluorescent phosphor. They are a very efficient source of illumination because nearly all the electricity is turned into light, unlike a traditional incandescent light bulb, which turns most of its incoming energy into heat.
leetspeak (from “elite speak”) written slang that modifies words by replacing letters with symbols or digits to make them look more computerish, using phonetic spellings, and adopting common typing errors as conventions.
A familiar example is the spelling of elite as leet or |33t. It is common to see 3 for E, 1 for I, and @ or 4 for A. There is almost infinite
281 |
letter size |
variation in the ways that ASCII characters can be used creatively to form letters, and so there is no official dictionary of leetspeak; people make it up as they go.
Although leetspeak was originally used to exclude the uninitiated and to bypass chat room filters that block dirty words, it is now most frequently seen in jokes.
left-click to CLICK with the left-hand mouse button (or the right-hand button if the mouse is set up for a left-handed person).
legacy anything left over from a previous version of the hardware or software. For example, legacy applications are applications from earlier versions of DOS or Windows; legacy hardware is hardware that does not support
legacy-free not burdened by the need for compatibility with substantially older equipment or software. Microsoft is promoting legacy-free PC design as a way to make PCs more reliable and easier to upgrade.
Since 1984, the IBM PC AT architecture has reserved a number of port addresses, interrupt request (IRQ) numbers, and memory addresses for various purposes. These were assigned long before sound cards, video capture devices, and other modern computer peripherals were invented. Because of this, the person installing a sound card into a modern PC often has to choose memory addresses and IRQ numbers for it—a job that should be left to the designer of the machine. Legacy-free PCs break free of these requirements by allowing the operating system to control the hardware directly. Legacy-reduced PCs are intermediates between legacy-free and conventional PCs. See also IRQ; PC 2001; PLUG AND PLAY.
legal size the size of paper used for legal documents in the UnitedStates, 81⁄2 × 14 inches. Contrast EXECUTIVE SIZE; LETTER SIZE. See also PAPER SIZES.
Lenovo company that bought IBM’s personal computer division in 2005 (web address: www.lenovo.com/us/en).
letter size the size of paper used for business letters in the United States, 81⁄2 × 11 inches. Elsewhere, ISO size A4 is the nearest equivalent.
Contrast EXECUTIVE SIZE; LEGAL SIZE. See also PAPER SIZES.
FIGURE 151. Legaland letter-sized paper
letterspacing |
282 |
letterspacing the space between letters (characters). See Figure 152. Look for the letterspacing controls with other FRAME attribute commands (letterspacing is sometimes called TRACKING).
FIGURE 152. Letterspacing
LF (line feed) the character code that tells a printer or terminal to advance to the next line; ASCII code 10. UNIX uses LF to indicate the end of a line in a text file. The Macintosh uses CR; Windows uses CRLF. See CR; CRLF. Contrast FF (form feed).
Li-ion (Lithium-ion) a type of rechargeable battery widely used in portable computers. They have higher capacity than NiCd and NiMH batteries but are more expensive and require different charging circuitry. See
NICAD, NICD; NIMH.
library
1.a collection of files, computer programs, or subroutines. A loader library is a file containing subroutines that can be linked into a machine language program.
2.a collection of reference materials and software tools, such as clip art, prerecorded sounds, and predefined objects.
license permission to use patented or copyrighted material. See PER COM-
PUTER; PER SEAT; PER USER; SHRINKWRAP LICENSE; SOFTWARE LICENSE.
LIFO (last-in-first-out) a STACK (definition 1); a data structure or memory device from which items are retrieved in the opposite of the order in which they were stored. Contrast FIFO.
ligature a printed character representing a combination of two or three letters (Figure 153). Some of the most sophisticated word processing programs, such as TeX, change pairs of letters into ligatures automatically.
FIGURE 153. Ligatures
light
1.visible electromagnetic radiation.
2.type that is designed and drawn with very fine strokes; the opposite of BOLD.
283 |
limits of computer power |
3. (in 3D and animation software) virtual device that mimics the effect of real light upon the computer-generated scene. Computer lights can be adjusted in many of the same ways as their real-life counterparts: intensity, position, direction, and color. See also AMBIENT LIGHTING.
light-emitting diode see LED.
light pen a pen-like light-sensitive device that can be used like a mouse to communicate with a computer. The operator holds the pen up to the screen, and the computer can sense what point on the screen the pen is touching. Light pens were popular in the 1970s but have largely been replaced by mice.
limitcheck PostScript error that occurs when a drawing is too complex to be printed.
limits of computer power things that computers cannot do, which is a subject of continuing theoretical study.
Computers can perform only tasks that can be reduced to mechanical procedures (algorithms). They are therefore inapplicable to tasks that cannot or should not be reduced to mechanical form, such as judging the greatness of a work of art or administering psychotherapy. Rather surprisingly, however, there are some tasks that are mathematically precise but that pre- sent-day computers cannot perform. These fall into two major types: (1) problems with no known algorithmic solution, and (2) problems whose best known algorithmic solutions require unreasonable amounts of time.
An example of a problem of the first type (one with no presently known algorithmic solution) is how to get a computer to recognize the structures of sentences in a human language such as English. Obviously, this is something computers will have to be able to do if we are ever to be able to communicate with them in English, and there is no reason to think it impossible. The difficulty is simply that English (and all other human languages) are so complicated that complete algorithms for processing them have not yet been discovered.
A good example of the second type of problem, one that takes an unreasonable amount of time to solve, is the so-called traveling salesman problem. The task is to find the shortest route by which a salesman can visit a particular set of cities (in any order). The only known way to solve this problem is to try all possible routes. A few shortcuts are possible—for instance, the testing of each route can be abandoned as soon as its length exceeds the shortest length already found, without pursuing it to the end— but the number of steps is never substantially fewer than N factorial, where N is the number of cities (see FACTORIAL). Suppose the fastest imaginable computer could perform one step in this algorithm by moving an electric charge a distance of 1 millimeter at the speed of light. This would mean that it could perform 3 × 1011 steps per second. Then the times required to solve the traveling salesman problem (in N! steps) would work out as follows:
Lindows, LindowsOS |
|
284 |
|||
|
|
|
|
|
|
|
Number of |
Number of |
Time |
||
|
|
Cities |
Steps |
Required |
|
5 |
120 |
0.36 picosecond |
|||
10 |
3,628,800 |
12 microseconds |
|||
15 |
1.3 × 1012 |
4.4 seconds |
|||
20 |
2.4 × 1018 |
94 days |
|||
25 |
1.6 × 1025 |
1.6 million years |
|||
30 |
2.7 × 1032 |
2.8 × 1013 years |
|||
And this is with a computer millions of times faster than any that presently exist. Obviously, it will never be feasible to solve the traveling salesman problem for more than a few cities unless a much better algorithm is found.
Another interesting class of computational problems, known as NPcomplete problems, has been proved to be equivalent to the traveling salesman problem; if a better algorithm is found for any NP-complete problem, it will be applicable to all of them.
See also CHURCH’S THESIS; COMPLEXITY THEORY.
Lindows, LindowsOS the original name of LINSPIRE; it was changed to avoid infringing Microsoft’s trademark rights to the name Windows.
line
1.in geometry, the shortest path connecting two points. A geometric line is always perfectly straight and has no width.
2.in graphics, a visible representation of a geometric line. A line in this sense has a definite color and width (normally at least 0.5-point for good visibility on paper; see HAIRLINE) and may be continuous, dashed, or dotted.
3.a printed line of type. Text is most readable with a line length of about 65 characters. See also LINESPACING; WORD WRAP.
4.an electronic communication path, such as a telephone line. See T1
LINE; T3 LINE.
line cap the end of a drawn line. In most DRAW PROGRAMs, you can choose square or rounded ends, or even arrowheads.
line drawing an illustration that can be represented as a series of hardedged black lines and black areas on a white background. Line drawings are easily converted to vector images by tracing them. Contrast
GRAYSCALE and PHOTOGRAPH.
line feed the character code that tells a printer or terminal to advance to the next line; ASCII code 10. UNIX uses LF to indicate the end of a line in a text file. The Macintosh uses CR; Windows uses CRLF. See CR; CRLF.
line in (on a sound card) line-level audio input. See LINE-LEVEL.
line-level (describing an audio signal) a signal level of about 0.1 to 1 volt, designed to connect to the input of another amplifier. Some line-level outputs can drive headphones; others cannot.
285 |
linked list |
Speaker-level audio is a slightly higher voltage, but the main difference is that speaker-level outputs can deliver much greater current (amperage) in order to drive speakers. Microphone-level audio is a much lower level, about 0.001 volt.
line out (on a sound card) line-level audio output. See LINE-LEVEL.
line printer a type of IMPACT PRINTER that prints an entire line of type at once, formerly used on mainframe computers.
line spacing the spacing in between lines of type. Also called LEADING.
linear fill a way of filling an object with color so that it makes a smooth transition from one color at one side of the object to another color at the other side. You can specify the angle of the linear fill. Contrast
FIGURE 154. Linear fill
link
1.any kind of communication path between two computers.
2.an entry in one directory or menu that points directly to something in some other directory or menu; a SHORTCUT. Links can be used to make the same file accessible from more than one directory or to put the same program on more than one menu.
3.an item on a WEB PAGE which, when selected, transfers the user directly to some other web page, perhaps on a different machine. Also called a
HYPERLINK. For example see HTML.
4.in Windows, an OLE communication path between programs. See OLE.
5.to combine the machine instructions for a program with the machine
instructions for any predefined procedures that it uses. For example, a program that does trigonometric calculation might use predefined procedures to find sines, cosines, and tangents. Some compilers perform linking automatically; others require you to execute a linker as a separate command.
6. a pointer in a linked list or tree. See LINKED LIST; TREE.
FIGURE 155. Linked list
link, dead see
linked list a way of organizing data items in a computer so that they are retrievable in a particular order that is not necessarily the same order as