L1 cache
Level 1 cache. Aka primary cache. Memory cache built into the microprocessor chip. See also cache.
L10n
Localization. "L" + 10 letters + "n". Note that it starts with an upper case L so it is not confused with the number 1 immediately following.
L2 cache
Level 2 cache. Aka secondary cache. Memory cache in a separate chip from the microprocessor chip. See also cache.
LAB Color
Lightness-A-B Color. An international color standard developed by the Commission Internationale d'Eclairage (CIE) as an alternative to RGB and CMYK. Its color channels are intensity of white, and two colors of choice, A and B.
LAMP
Linux/GNU OS, Apache web server, MySQL database, PHP/Python/PERL programming language. A no- or low-cost, open-source web and database system, especially one created using the specified technologies. The beloved Wikipedia.org uses LAMP where P = PHP. See also WISP. See OnLAMP.com by O'Reilly.
LAN
Local Area Network. Computers linked within a local area, usually no more than a few hundred meters, so they can interoperate and share resources. The computers are either peer-to-peer or at least one server with clients. The hardware connections usually involve a network interface card on each computer, cabling, and sometimes different hubs and routers.
 
There are several standard ways to build LANs. In the order of popularity, the most common ways are Ethernet (10 Mb/s), token ring (4-16 Mb/s), and ARCnet.

Networks that exceed the scope of a single physical network are considered to be WANs (Wide Area Networks). A WAN can be said to be interconnected LANs.
laser

Light Amplification by Stimulated Emission of Radiation. A device which produces a coherent (same wavelength) beam of photons (light).

Light typically bounces around an amplifying medium (some solid, liquid or gas). The first amplifying medium used for laser was ruby (crystalline alumina or Al203) where some of Al ions were replaced with Chromium ions (Cr3+). The gain is not constant with the medium but depends on the wavelength of the incoming light, the length of the medium, and the extent to which the energy of the medium is pumped up. The medium may be pumped up with additional irradiation, by laser, by electrical current.

On both ends of the device containing the amplifying medium are mirrors. The mirrors serve to provide positive feedback by returning some of the beam back to the medium for further amplification and oscillation. The mirrors also ensure the coherence and parallelness of the beam. The space between the mirrors is the laser cavity, it should be tuned as one would a guitar string. One mirror is fully reflective, the exit mirror is 20 to 98% reflective. The exit end of the medium's container may be inclined to produced a polarized beam.

In absorption of a photon, an atom goes into a high energy state. In spontaneous emission it releases a photon when it returns to a low energy state. In a stimulated emission, an atom already in a high energy state is struck by a photon, causing it to release two photons as it returns to a low energy state. In addition, the two photon are in phase, i.e. in sync. For stimulated emission to occur, population inversion must occur. This is a non-normal condition where more atoms are excited than not.

The gain of the laser is the factor by which the intensity of the light is increased.

laser printer
A printer which usually produces images finer than inkjet printers. A laser printer that takes the print data, creates a bit-mapped image, and transfers it to a photostatically sensitive medium such as a drum or belt. A laser passes over the medium and charges the exposed areas. The pattern of electrical charge is transferred either through or onto the paper. The areas attract toner, a finely ground plastic, which is then fused onto the sheet.
latency
The amount of time it takes for something to happen in a system. This can refer to processing, accessing, or transfer time. In networks, the bandwidth and latency define the capacity and speed of a network.
LaTeX
See TeX.
lazy evaluation
Minimizing the work that  a computer has to do in a program. Lazy evaluation has two implementations: minimal evaluation and delayed evaluation.

In minimal evaluation (aka short circuit evaluation), parts of an expression are evaluated until the final value of the expression is known. EG: In C: if (bln && myFunc(x)) { ... }; If bln is false, then there is no need to evaluate myFunc(x). This is useful if latter parts of an expression are more processing intensive or rarely used.

In delayed evaluation, an expression is not evaluated when it receives a variable, but only when a value from the expression is needed. EG: If an expression produces an infinite list, but only the nth value is needed, the expression is only calculated to that nth value. This is useful especially in functional programming.
LDAP
Aka X.500-lite. An open set of protocols for accessing information directories. LDAP was based on X.500 but it is simpler and supports TCP/IP. LDAP should allow almost any application to access directory information such as e-mail, addresses, and public keys.
leading
(Rhymes with wedding.) The space between lines of text as measured from baseline to baseline. Leading is sometimes adjusted to increase legibility. Originally this referred to slabs of lead or lead-like metal placed between rows of die cast letters used in old presses. A rule of thumb is to use leading that is 1.1 times the font height; for headlines, a tighter leading looks fine.
legacy
Refers to old data, hardware, or software that is getting out of date but is still functional and is difficult and/or expensive to update.
Lenna
One of the most widely used standard test images for image compression algorithms. The image is a portion of the centerfold of the 1972-11 issue of Playboy magazine, which incidentally, was one of their best selling issues ever. The model was published as "Lenna Sjööblom", but her Anglicized name is "Lena Soderberg" and her actual Swedish name is "Lena Söderberg".
The Lenna standard test image The standard test image.
The full Lenna centerfold The full centerfold.
LF
Line Feed. ASCII decimal code 10. VB chr(10). A CR indicates the end of a line while LF indicates a new line. It is common to use both CR and LF.
LIFO
Last-In, First-Out. See stack.
ligature
Two characters that have been blended together to form one character. EG: "encyclopedia" is sometimes spelled "encyclopaedia" (encyclopædia) with the contiguous "a" and "e" blended together. ff, fi, fl, ffi, and ffl are common word groups that are formed into ligatures.
Lightweight Directory Access Protocol
See LDAP.
LIMDOW
A technology that speeds the writing of a CD-ROM. Unlike the conventional magnetic-optico (MO) technology which passes the disk twice under the head (once to erase and a second time to write), LIMDOW technology modulates the intensity of the laser to erase and write in one pass.
line feed
See LF.
lines per inch
See lpi.
Linotronic
See image setter.
Linux
An operating system that is starting to edge in on the popularity of the Windows OS. Linux is free and open source variation of the  UNIX OS that runs on nearly any kind of microprocessors. It was Linux Torvalds who created the original Linux kernel when he was a student at the University of Helsinki in 1991. Linus Torvalds created the original Linux kernel when he was a student at the University of Helsinki, Finland in 1991. Linux is now developed by thousands of developers worldwide.

The top five variations (aka distributions or versions) as of 2000/04 are:
  • OpenLinux by Caldera
  • RedHat Linux by RedHat Software
  • TurboLinux by TurboLinux
  • SuSE Linux by SuSE Linux
  • Debian GNU/Linux by Debian
The official website for all things Linux is www.Linux.org. See also my section on Linux-UNIX.
Listserv
A program on a mail server that manages an e-mail list on a particular topic.
literal
The information, the constant, the value represented by a variable, eg $text = "Johnny be good", where $text is the variable and "Johnny be good" is the literal. Literals are actual text and numbers as opposed to calculated values. Variables and their literals are also usually of a particular type, eg boolean, number, or string variables.
little-endian
See big-endian.
Livescript
See JavaScript.
LLC sublayer
Logical Link Control sublayer. A sublayer of the Data Link Layer of the OSI Reference Model. It deals with the sending and receiving of packets and checking for parity. EG: IEEE 802.2 deals with Ethernet's LLC sublayer.
LMDS
Local Multipoint Distributed Service. Aka wireless cable. Aka wireless broadband. Data broadcasting at high frequencies (the millimeter sized microwave band at 2.4 GHz). This involve line of site transmitters and receivers. The signal is boosted to avoid "rain fade", the loss of signal due to water in the air, i.e. humidity.
Local Area Network
See LAN.
Local Bus
A direct path from the CPU allowing a controller card or video card to communicate as fast as the CPU operates. It is usually either VESA (32 bit) or PCI (64 bit).
Local Multipoint Distributed Service
See LMDS.
local variable
A variable whose scope is only within the function that declared it. See also global variable.
lock
To make a file or portion of a file inaccessible to other users while the current user is utilizing it.
logic error
A runtime error made when the program has proper syntax but does not produce the desired result due to improper reasoning by the programmer.
logical
(1) Relating to binary computations where the variables and operator deal with values that are either true (1) or false (0). The common logical operators are NOT, AND, OR, XOR, EQV, and IMP. Here are their truth tables:
NOT  B  =  Result
     0     1
     1     0

A  B | AND  OR  XOR  EQV  IMP
0  0 | 0    0   0    1    1
0  1 | 0    1   1    0    1
1  0 | 0    1   1    0    0
1  1 | 1    1   0    1    1

(2) See virtual.
Logical Link Control sublayer
See LLC sublayer.
Logical Unit
See LU.
LOL
Laughing Out Loud.
Lorem Ipsum
'Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book.' See also LIpsum.com, The Straight Dope on Lorem Ipsum.
lossless
When the object, data, info, etc. is compressed and keeps its full integrity when uncompressed. EG: If I open a picture file, save it, open it again, then the process was lossless if no data was lost and it looks exactly the same --otherwise the process was lossy if data was lost and the image may now look fuzzier. Lossy compression may vary from imperceptible to glaringly obvious.
lossy
See lossless.
low-level language
Aka machine language. A programming language that is binary and can be directly understood by a computer without needing to be compiled first. See programming languages.
Low Voltage Differential Signaling
See LVDS.
lpi
lines per inch. Refers to the number of gridlines in a halftone screen. See resolution.
LPT
Line Printer Terminal. This is refers to the printer port. An operating system may also use LPT to identify a printer. See also port.
LTNS
Long Time No See.
LU
Logical Unit. An SNA term for the items used to communicate with other SNA units. A LU can be an actual printer or terminal, or it can be a program.
lurk
To view mailing lists, newsgroups, bulletin board discussions, chat rooms, IRCs, etc., without actively contributing or participating.
luser
Derogatory term for a computer loser user.
LVDS
Low Voltage Differential Signaling. A low noise, low power, and low amplitude method for high speed (Gb/s) data transfer over copper wire. LVDS has a dual wire system at 180 degrees which enables easier and more effective filtering of noise. LVDS relies on positive, zero, or negative voltage for data transmission instead of actual voltage level thus allowing greater lengths of wire. LVDS voltage is 3.3 or 1.5 volts instead of the standard 5 volts. The usage of LVDS allows high speed systems to use fewer wires. EG: Ultra Wide (UW) and UW-2/3 SCSI to use only 68 wires.
Lynx
A text-based browser. The client Lynx app is only a dummy terminal. The real Lynx app is on your ISP and that Lynx app is the one that hits the desired web pages, parses them, and then sends the client just the text. It's very fast but then again it's text based.

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