This is part three of the series called, "ROM's Glossary for the Atari." Since I will not likely have all the definitions, I would very much appreciate hearing from whoever could add to my list.


    Label: A name attached to an instruction or statement in a program that identifies the location in memory of the machine language code or the assignment produced from that instruction or statement.
    Least Significant Bit: The rightmost bit in a group of bits, that is, bit 0 of a byte or a 16-bit word.
    Line: In BASIC, a line consists of one or more BASIC statements preceded either by a line number in the range of 0 to 32767, or by an immediate mode line with no line number.
    Low Level Language: A computer language that the computer can execute directly with no translation other than numeric conversions.
    LSI: Acronym for Large Scale Integration. This refers to a technology for manufacturing silicon chips. LSI chips are the largest and most powerful chips in mass production: they contain many thousands of components.
    Luminance: Atari's term for brightness, it is the lower nybble of a color register's color. In the BASIC `Setcolor' command, the third operand is the luminance. There are eight even-numbered values for luminance ($0 to $F, even values only) which, in combination with hue values, produce the 128 colors available on the Atari computers.
    Machine Language: The programming language that the computer can execute directly with no translation other than numeric conversions.
    Map Mode: This is a specific type of ANTIC display mode using simple colored screen pixels instead of characters for the screen display. There are eight ANTIC map modes with varying degrees of resolution. Six of these are callable from BASIC.
    Mark: The 1 state on a serial data communications line. For cassette I/O, this is a 5327-Hz frequency.
    Marker Character: For cassette I/O, this is 55 (hex) value, whose purpose is to adjust the baud rate. Including the start and stop bits, each marker character is 10 bits long.
    Memtop: In BASIC, a pointer ([90,9] decimal) to the top of application RAM, the end of the user program. Program expansion can occur from this point to the end of free RAM, which is defined by the start of the display list. This Memtop is not the same as the OS variable called Memtop.
    Memory Map: A memory map is a description of where things are in memory. Having one of these handy is essential when one is doing any type of programming.
    Missile: In Player/Missile Graphics, each player has an associated missile. This means there is a maximum of four missiles. A missile is a one-dimensional image in RAM used in player-missile graphics and is 2 bits wide.
    Mode Line: A collection of horizontal scan lines for screen displays. Depending upon the BASIC or ANTIC display mode in effect, a mode line will be composed of varying numbers of scan lines. By the same token, depending upon the display mode, a screen image will be composed of varying numbers of mode lines.
    Modem: A device that adds or removes a carrier frequency, thereby allowing data that is to be transmitted on a high-frequency channel to be received from such a channel.
    Module: A part or section of a program.
    Monitor: A program in ROM that handles both the system power-up and SYSTEM RESET sequences. This program allows the computer user to enter programs and data, to run programs, to examine contents of the computer's memory and registers, and to utilize the computer's peripherals.
    Most Significant Bit: The leftmost bit in a group of bits, that is, bit 7 of a byte or bit 15 or 16 of a bit word.
    Murphy's Law: the famous maxim that "whatever can go wrong, will."
    Narrow Playfield: A screen display width option equal to a width of 128 color clocks.
    Nesting: Constructing programs in a hierarchical manner with one level contained within another, and so forth. The nesting level is the number of transfers of control required to reach a particular part of a program without ever returning to a higher level.
    Nibble (or nybble): A unit of four bits. A byte (eight bits) may be described as consisting of a high nibble (four most significant bits) and a low nibble (four least significant bits).
    NMI: Non-Maskable Interrupt (i.e., cannot be disabled by the 6502). The Display List Interrupt and the Vertical Blank Interrupt are both NMIs. These can be disabled with the ANTIC NMIEN register.
    NMIEN: The Non-Maskable Interrupt Enable Register which controls enabling of various NMI interrupts such as the Display List Interrupt (DLI).
    Normal IRG Mode: In cassette I/O, this is a mode where the tape always comes to a stop after each record is read. If the computer stops the tape and gets its processing done fast enough, the next read may occur so quickly that the cassette deck may see a slight dip in the control line.
    Normal Playfield: A screen display width option equal to a width of 160 color clocks.
    Object Code: The code produced by a compiler or Assembler program. It can be directly understood by the Atari computer without using a language such as BASIC as a translator.
    Object Program: A program that runs directly on the Atari computer. An object program, created by an Assembler or a language such as ACTION! uses the actual numeric instruction code of the Atari's 6502 microcomputer chip.
    Open (a file): Make a file ready for use. The user generally must open a file before working with it.
    Operator: In BASIC, any one of the 46 tokens that in some way move or modify the values that follow them.
    Operator Stack: In BASIC, a software stack where operators are placed when an arithmetic BASIC expression is being evaluated.
    Operating System (OS): A computer program that controls the overall operations of a computer and performs such functions as assigning places in memory to programs and data, scheduling the execution of programs, processing interrupts, and controlling the overall input/output system. It is also known as a monitor, executive, or master-control program, although the term monitor is usually reserved for a simple operating system with limited functions.
    Overflow: The result of the arithmetic operation is too large for the register specified. The sign bit is filled from the next lower bit, and a status flag is set.
    Overscan: The `spreading out' of a television image by the raster scan method of display so that the edges of the picture are off the edge of the television tube. This guarantees no unsightly borders in the television picture.
    Page: A subdivision of the memory. In 6502 terminology, a page is a 256-byte section of memory in which all addresses have the same eight most significant bits of a memory address.
    Page Flipping: A method of changing screen memory pointers in order to change the current screen display. The common methods of displaying data on the screen involve PRINTing or POKEing data. With page flipping, screen images are stored in various pages of RAM, and then pointers are changed that tell the computer to get its screen data from the desired RAM locations, rather than redrawing onto the screen.
    Paddle: A piece of equipment used for games and drawing on the screen. The uses to which it can be put include axis position for accuracy.
    Parallel Interface: An interface between a CPU and input or output devices that handle data in parallel (more than one bit at a time).
    Parameter: An item that must be provided to a subroutine or program in order for it to be executed.
    Pascal: A structured computer language descended from ALGOL 60. Added features include "records" (data structure definition) and "sets." It is suitable for a wide variety of chores from systems to application programming. A stripped-down version of Pascal for the Atari, `Draper Pascal,' by Draper software, is a good place to start if you wish to learn Pascal.
    Peripheral: Any external device connected to a computer and controlled by it.
    PIA: Acronym for Peripheral Interface Adaptor. This is an LSI chip which interfaces the 6502 with external devices. The joystick pins of the two or four user ports are connected to a PIA inside the computer.
    Pirate: This term is given to a person who illegally trades, buys or sells copyrighted merchandise. In the computer industry, this usually involves stealing software through copying cassettes or disks.
    Pixel: The smallest screen graphics unit addressable in a particular display mode. It is a square whose size depends on the display mode.
    Player: A one-dimensional RAM image used in player-missile graphics which can be 128 bytes (double-line resolution) or 256 bytes (single-line resolution) long. The player appears as a vertical band 8 pixels wide stretching from the top of the screen to the bottom. There is a maximum of four or five independent players, depending upon whether you combine the missiles or not.
    Player Color: The color of a player in player-missile graphics. Each of the four independent players has its own color stored in its associated color register.
    Pointer: A data item whose contents are the address of another data item.
    Port: The basic addressable unit of the computer's input/output section.
    Programming Language: A set of rules specifying a language that can be translated into Machine Language and cause the computer to carry out functions. These include ACTION!, Atari Microsoft Basic, Atari Basic, Basic A MAC 65, Macro-Assembler, Pilot, Synassembler, and Valforth.