"The Atari A to Z" by Mark S Baines Copyright (c) 1998 Mark S Baines All Rights Reserved YOU MUST READ "READ_ME.NOW" BEFORE YOU LOOK AT ANY OF THIS FILE ***************************************************************************** L Label A character string that identifies a sequence of instructions in some language's source code that may be entered with its first instruction as the entry point. Also, self-adhesive paper with identifying information to attach to disks etc. LAN Local Area Network. Landing zone On Winchester magnetic hard disks, a band on the surface where the read/write heads takes off from and land on when at rest and no data transfer or track seeking is taking place. Landscape The orientation of a document where it is wider than it is tall. Language A computer, source or programming language is an artificial one designed for use by humans in instructing machines where a structure and syntax is necessary to prevent ambiguous constructions. A source language is a language in which programs are written so as to control the operations of a computer. They may be either a 'high-level' or 'low-level' language. High-level languages, such as C, BASIC, Pascal, are designed for ease of use in writing programs and are intended to be portable across different systems. A whole sequence of computer operations can be performed from one simple instruction, hence the term 'high-level'. Low-level languages require the programmer to instruct the computer very explicitly, a step at a time, typically in a non- portable language, such as an assembler or assembly language. Instructions in a high- or low-level language are translated into object code which is also called machine code or object language. Sometimes an intermediate language is used when translating a high-level language into machine code. Language processor A program that performs some or all of the steps of producing object code from source code. The term applies to compilers, assemblers, translators and interpreters. LAN port The Mega STE, TT and Falcon030 have a SCC serial port especially configured to operate as a LAN connector using an 8-pin female mini-DIN socket. The Zilog 85C30 SCC chip supports two ports, A and B, where Port A can be used as the Local Area Network port or as a low-speed RS-232C port, the output being directed to the appropriate connector (when bit seven of the PSG sound chip Port A is zero, LAN mode is selected). On the Falcon the SCC Port A is always connected to the LAN port. The LAN implementation is synchronous and some heavy duty buffers (28LS30) are used to enable the SCC chip to drive long cables of around 50 metres. There is DMA support to allow a fast throughput. The LAN port claims to have Apple Local-Talk compatibility. No software drivers are available for a network using this port at the time of writing. LAP-M Link Access Procedure for Modems. A de facto standard for data compression on duplex data communication links, giving a 4:1 compression ratio, whereas MNP 5 only gives 2:1. This standard was incorporated into the CCITT V.42 and V.42bis protocols. Large scale integration - LSI Semiconductor devices with between 100 and 1,000 logic gates formed on a single silicon chip. Laser Light Amplification by Stimulated Emission of Radiation. A device that produces a single frequency light beam with parallel waves. It has the property of being able to be focused on a very small area over any distant, the waves not diverging as with ordinary light. Large amounts of energy can be transmitted at the cost of relatively little power. Laser printer A printer using a laser beam to write characters onto a selenium coated drum, electrostatically charging the surface which is then coated with toner which adheres to the charged areas. Paper is rolled across the drum and heated thus melting the resin and fixing the ink to the paper. These printers produce excellent quality output, (usually at 300 x 300 dots per inch), are fast, quiet and versatile. The cost of laser printers has decreased considerably in the past few years. 600 dpi printers are now freely available. Latency In disks, the time taken for the required sector to rotate under the disk head after the read command has been received. Launch Synonymous with Run. Laws With tongue in cheek... The Laws Of Computer Programming: Any given program, when running, is obsolete. Any given program costs more and takes longer each time it is run. If a program is useful, it will have to be changed. If a program is useless, it will have to be documented. Any given program will expand to fill all the available memory. The value of a program is inversely proportional to the weight of its output. Program complexity grows until it exceeds the capability of the programmer who must maintain it. Pierce's Law: In any computer system, the machine will always misinterpret, misconstrue, misprint or not evaluate any maths or subroutines or fail to print any output on at least the first run through. Corollary To Pierce's Law: When a compiler accepts a program without error on the first run, the program will not yield the desired output. Osborn's Law: Variables won't; constants aren't. Troutman's Postulate: Profanity is the one language understood by all programmers. Not until a program has been in production for six months will the most harmful error be discovered. Job control cards that positively cannot be arranged in improper order will be. Interchangeable tapes won't. If the input editor has been designed to reject all bad input, an ingenious idiot will discover a method to get bad data past it. If a test installation functions perfectly, all subsequent systems will malfunction. Hall's First Law: If people built houses the way we write programs, the first woodpecker would wipe out civilization. Sattinger's Law: It works better if you plug it in. Jenkinson's Law: It won't work. Horner's Five Thumb Postulate: Experience increases directly with equipment ruined. Cheop's Law: Nothing ever gets built on schedule or within budget. Rule Of Accuracy: When working toward the solution of a problem, it always helps if you know the answer. Westheimer's Rule: To estimate the time it takes to do a task: estimate the time you think it should take, multiply by two and change the unit of measure to the next highest unit. Thus, we allocate two days for a one hour task. Stockmayer's Theorem: If it looks easy, it's tough. If it looks tough, it's damn near impossible. Brooke's Law: Adding manpower to late software makes it later. Finagle's Fourth Law: Once a job is fouled up, anything done to improve it will only make it worse. Featherkile's Rule: Whatever you did, that's what you planned. Flap's Law: Any inanimate object, regardless of its position, configuration or purpose, may be expected to perform at any time in a totally unexpected manner for reasons that are either entirely obscure or else completely mysterious. Layout The arrangement of text and images on a page. LCD Liquid Crystal Display. A common 'segment' display as used in watches and calculators and portable computers. It uses sandwiches of polarizing screens, liquid crystal layers and tiny transparent metal conductor layers to make the image. They require very low voltages and are inexpensive and reliable. They are also flat and light being more suited to portability than CRT displays. Greyscale and colour LCD displays are now available. Lead or Leading Rhymes with 'said'. Traditionally, metal strips used to space lines of text in print and therefore a measurement of the distance between two lines of text. In some DTP programs it has come to mean the distance between the baselines of two lines of text, that is, the height of the font characters and the space between the lines. For example, '8 on 10' means an eight point font with two points of leading. Leader A string of characters, usually dots, used to guide the reader's eye across the page, as in a Contents page. Leaf In a tree structure, an owner with no members. In printing, a single sheet with one page on each side. Leased line A telephone line that is permanently connected for continual data transmission. Least significant bit - LSB In a bit-group, the bit at the farthest right position having the least weight and transmitted first. Least significant byte - LSB In a group of bytes (a word or long word), the byte that is at the farthest right position having the least weight. Least significant digit - LSD The digit in the farthest right position with the lowest weight. LED Light Emitting Diode. A semiconductor device producing light by electroluminescence when a current is passed through it. They are used as indicator lights, in some segment displays and as a light source in fibre optics. They are more visible in ambient light than LCDs but require more power and are difficult to build into compact high resolution displays. Left shift To move the contents of a memory location in increments to the left. With numeric data, it has the effect of multiplying the number by the radix or base (usually two in computers, the base of binary numbers). Legal Recognizable by the system. LF Line Feed. LHARC A file compression format with the .LZH or .LHA file name extender. Universally available and popular with later varieties producing high compression rates and fast processing speeds. Library One or more files of frequently used source or object code routines to be linked into a program upon compilation. LIFO Last In First Out. An algorithm used to determine the order of use of some items, such as program variables, and forming the structure of a stack. See FIFO. Light pen A hand-held photosensitive stylus that detects light from a display screen as the electron beam scans it and identifies places on the screen for manipulation. Light pens are awkward and uncomfortable to use after a period of time, their use as pointing devices being largely replaced by the mouse. Limit The minimum or maximum permissible value in a range. Line A transmission medium, usually wires, and equipment for carrying speech and/or data between separated locations. In print, a horizontal string of characters or dots on screen or paper. Line-A emulator This is the low-level interface to the ST's GEMDOS VDI routines containing the graphics primitives used by the VDI, such as plotting pixels, drawing lines and boxes and BLiTting. Line-A routines could be called from machine code by executing a special instruction, a word beginning with $A00n, where n is the number of the required routine and hence the name, Line-A. This interface is generally inconsistent, difficult to use and completely non-portable to other GEM environments. Support for Line-A routines was dropped with the introduction of the new video modes of the TT. They should not be used by programmers seeking TT and Falcon compatibility. Line-F emulator A TOS routine that replaces frequently used command sequences with just one command. Line art Vector graphics produced by a 'drawing' program, such as GEM metafiles, (as opposed to bitmapped images produced by painting programs) for inclusion into DTP articles. See GEM metafile. Line density The number of lines per vertical inch on a display or in print. Line driver Software or hardware that controls communications functions, such as bit- serial to bit-parallel conversion and character buffering. Line feed - LF ASCII character 10 causing an upward movement of paper in a printer or text on a screen corresponding to one line. Line noise The disruptive interference (usually white noise) on a telephone line that corrupts data. Line printer A printer that prints a line at a time rather than a character (dot matrix) or a page (laser) at a time. Such printers are rarely found today outside of specialist sectors. Line protocol A set of procedures and rules that control the interchange of data in a communications link. These include the code to be used, error correction and data compression techniques, the speed of data transmission, block lengths, control characters to be used etc. Line spacing The number of lines to a vertical inch of print or display. The normal line density on most character or line printers is 6 lpi. Line speed The data transmission speed of a line measured in bits per seconds or its Baud rate. Line transition In data communications, a change in one of the possible data significant conditions (frequency, phase, amplitude, line voltage) that can be produced by transmitting equipment and detected and interpreted by receiving equipment. See Baud. Link In communications, synonymous with a line or circuit although the term often refers to the data carrying facility rather than the hardware. In databases, using pointers or a table to establish access paths between records of two different files. In programming, to join together object code files produced from compiled source code with the language's library routines to form an executable program. Linked list In programming, a list in which each item except the last holds a pointer to the next in sequence. Linker A linkage editor, a program that links object code files to form an executable file. LISP LISt Processing. An interpretive language developed at MIT in the early 1960s and used in processing symbol lists and developing and modifying high-level languages. It is a favourite language with those interested in artificial intelligence. List An ordered set of data items, such as an array. Also, to display program source code on a screen or output it to a printer. Listing Printed (to screen or printer) program source code for debugging and testing results. Listing paper Continuous stationery. Literal In program source code, items (usually within quotation marks) that are to remain unchanged during compilation appearing in output exactly as inputted by the programmer, such as a program's name. In printing, a misprint. Live Functional and in use. A wire or circuit holding a current of electricity. Liveware Human computer users interacting with the hardware and software! LLL Low-Level Language. LMC1992 National LMC1992 Computer Controlled Volume/Tone Control chip in the STE, TT and Falcon, used to provide volume and tone control of the stereo DMA sound production. Load To place program code or data in memory or processor registers prior to execution or to place a data medium (tape, disk) in a peripheral. Also, to make an electrical connection that causes the normal current to flow. Local Directly connected to a computer rather than to a distant one via a communications link. In programming, a variable or function defined and existing only in one block of a program. Local area network - LAN Computers or terminals directly connected with cable usually within the same building and sharing some or all of the same resources, such as programs and data as well as disks, printers and even memory. Each computer or point of connection is called a node. LANs have a serial connection and such a port is available on Mega STE, TT and Falcon computers - the SCC Port A. Local variable A variable defined and existing only in one block of a program. Its value is not stored between calls to that program block. Locate To perform a search. Location An addressable position in computer storage, usually referring to memory. Log To record events, times and data into a computer file or book. Also, an abbreviation for logarithm. Log in, Log on To begin a session on a network or remote computer by entering an ID and password. Log out, Log off To end a session on a network or remote computer by using the correct command. Logbase A function that returns the address of the base of the logical screen of the ST-Falcon range, the one onto which the GEM VDI draws. Normally this is the same address as returned by Physbase() but this is not required. See Physbase. Logic The science or art of reasoning correctly. In computing, the process of breaking down problems of reasoning and comparison to elementary operations which can be performed by electronic circuits and using Boolean algebra. Also, those hardware devices that perform manipulation and control, such as semiconductors. Logic array A semiconductor device used to perform a relatively complex operation. See PLA. Logic gate or circuit An electronic circuit that performs a logic operation. Logic level One of two available control voltages as used in most electronic devices, usually +5 V (logic high) and 0 V (logic low). Logic operation An operation in which one or more binary inputs are evaluated or compared in accordance with a rule of logic to produce a binary output. Logic operator Any of the operators AND, OR and NOT and their combinations. Logical device A virtual device, an operating system identification of a peripheral device that is not an identification of an actual device, e.g. drive B: on a single floppy ST. Logical device name An identifier by which a peripheral device is known to the operating system, e.g. B:. Logical drive A partition of a hard disk drive or a RAM disk which is assigned its own drive identifier or drive letter and which behaves like a separate disk drive mechanism. Logical unit number - LUN A SCSI controller has its own address or ID and a hard disk (or other device attached to it) its own ID called a LUN. If more than one SCSI controller is attached to a computer it has its own unique ID, from 0 to 7 and if more than one device is attached to it, it has its own unique LUN from 0 to 7 (although different devices on separate SCSI IDs can have the same LUN). Most SCSI devices, like embedded SCSI hard drives, used on a ST will have only one LUN, usually 0. See SCSI. LOGO A high-level language, graphically oriented and associated with education. LOL Lots Of Laughter or Laughing Out Loud. Commonly used shorthand in e-mail and other messages. Long, Long word A 32-bit (four bytes or two words) integer. Look up To read the contents of a location in a table or index as a step in finding the storage location of a unit of code or data. Loop A sequence of instructions that is executed repeatedly in order to perform a single operation on or with different operands, thus avoiding the need to write, compile and store multiple copies of that sequence. Loop body That part of a loop that performs the processing function. Loop control That part of a loop that performs the loop count and exit condition check, such as in the statement FOR i = 1 TO 10... NEXT i. Low The lower of two possible voltages in control and logic circuits. Low-level language A language designed to produce efficient programs (quick and small) without particular regard for their ease of use by programmers. They typically produce one program instruction for each source code instruction and are designed for particular processors or computers making them non-portable, e.g. assembly language. Low resolution On the ST, a resolution of 320 x 200 pixels with sixteen colours, now very dated compared to other computers, including the TT and Falcon. Low-speed In data communications speeds of less than 2,400 bits per second. Lower case Letters that are not capitals. LPI Lines Per Inch. A measurement of line spacing or density. LQ Letter Quality. A relative term used to indicate the quality of output of printers compared to that produced by good quality typewriters using preformed embossed metal type. It is normally applied to dot matrix printers where the formation of characters by small dots has only recently produced similar quality print. LSB Least Significant Bit or Least Significant Byte. LSD Least Significant Digit. LSI Large Scale Integration. LSTTL Low-power Schottky Transistor Transistor Logic. A family of logic chips which have improvements in speed and power consumption compared to the original TTL design. These are the most widely used logic chips. LTTL Low-power Transistor Transistor Logic. An early development of TTL logic chips which used less power. These have been replaced by ALSTTL chips which are faster. LUN Logical Unit Number. Lynx An Atari hand-held games console designed by Epyx in 1987 with a small 160 x 102 pixels 3.5 inch sixteen colour backlit LCD screen (from a total of 4,096 colours) which even allows for left-handed use. It has a clock speed of 16 MHz, 64 K RAM, four channel sound with an internal mono speaker and mono output to headphones and the capability to be linked to eighteen other Lynxes for multiplayer games via the ComLynx. The maximum game size is 8 Mb. The machine is run by two Epyx VLSI PLAs called SUZY and MIKEY which are 16- bit CMOS subprocessors one for graphics providing sprite scaling techniques and the other for sound and speech. MIKEY consists of a MOS 65C02 processor which is an 8-bit CPU with a 16-bit address space providing the sound engine of four channel sound with an 8-bit digital-audio controller for each channel. The range is 100 Hz to above human hearing and supports stereo with panning. MIKEY also provides a video DMA driver for the LCD display, system timers, interrupt controller and a UART for the ComLynx. SUZY is a dedicated BLiTTER unit and graphics engine. It offers drawing support, an unlimited number of sprites with collision detection and high-speed sprite scaling, distortion and tilting effects. It also offers the decoding of compressed sprite data, clipping and multidirectional scrolling, variable frame rate (up to 75 frames/second), the screen resolution of 160 x 102 (with artificially-induced 480 x 102 possible), a 4,096 colour palette with sixteen colours on screen at once and a maths coprocessor with a 16-bit multiply and divide, providing 32- bit answers and parallel processing of single multiply or divide instructions. The Lynx contains 64 K of 120 ns DRAM and 512 bytes of bootstrap and game card loading ROM. Game cards currently hold 128 K or 256 K of ROM, but in theory up to two megabytes can be stored with bank switching. With the six alkaline batteries, the reasonable average battery life is four to five hours. The Lynx can run with rechargeable NiCad batteries, but average battery life drops to one and a half hours per recharge. ComLynx communications run from 300.5 to 62.5 Kbps and works on a "listen and send" structure. Data transmission between Lynxes is done in the background, freeing up the CPU to run the game directly. It uses a three-wire cable (+5 V, Ground, Data) and allows for bidirectional serial communications. Messages are framed in 11-bit words, each consisting of a start bit, eight data bits, parity bit, and a stop bit. The ComLynx port is used only for communications, it cannot be used to control other aspects of the Lynx, although in theory it can be used to send signals to external devices. In 1992 the Lynx II was launched with a smaller case, an advertised clock speed of only 4 MHz (this is disputed and it seems that it is still 16 MHz) and 4 Mb game capacity. It has stereo sound through the headphones socket and the screen can be turned off while a game is paused to save on battery power. A power LED has been added which blinks when power is low and the cartridges are easier to insert. Game controls consist of an eight-direction joypad, two sets of fire buttons (A and B) and two option buttons (Option 1 and Option 2). Control knobs set the volume and screen brightness. Ports connect stereo headphones (mini-DIN 3.5 mm stereo), the multiplayer ComLynx cable and DC power (9 volts, 1 amp). Accessories include a battery pack, carry case and sun visor/screen, mains adaptor, car adaptor and ComLynx cable for multiplayer games. Although the Lynx has one of the best specifications of the hand held games consoles, it does not have the range of software that other competitors have. Ironically, the Lynx Developer's Kit consists of a Commodore Amiga. It has 3 Mb RAM and hard disk, a "Howard" board which is a parallel-interface module that has the Lynx electronics and debugging tools, and the "Howdy" unit which is a small PC board in a plastic case with buttons and a Lynx display connected to the "Howard" board. The software consists of Handy-Bug which is a symbolic debugger and disassembler, Handicraft - a graphics translator that turns Amiga IFF files into coded Lynx sprite data, HSFX - the sound editor, macro libraries, sample programs and system documentation plus updates. LZW compression Lempel, Ziv and Welch were the originators of this method of lossless file compression used particularly on image files, such as GIF and TIFF. The compression algorithm is based on RLE using variable length bit patterns and a dictionary to store the frequency of patterns which isn't stored with the compressed file. The compression efficiency is very high but decompression of the file takes longer than other lossless methods because the dictionary table has to be reconstructed each time. L 99 entries EOF