PAGE 256 bytes of memory which share a common high order address byte. Zero page is the first 256 bytes of memory ($0000 through $00FF). PARALLEL Opposite of serial. A communication mode which sends all of the bits in a byte at once, each over a separate line or wire. PARAMETER LIST An area of storage set aside for communication between a calling program and a subroutine. The parameter list contains input and output variables which will be used by the subroutine. PARITY A scheme, similar to checksums but on a bit level rather than a byte level, which allows detection of errors in a single data byte. An extra parity bit is attached to each byte which is a sum of the bits in the byte. Parity is used in expensive memory to detect or correct single bit failures, and when sending data over communications lines to detect noise errors. PARSE The process of interpreting character string data, such as a command with keywords. PATCH A small change to the object code of an assembly language program. Also called a "zap". PERIPHERAL A device which is external to the computer itself, such as a disk drive or a printer. Also called an Input/Output device. PHYSICAL RECORD A collection of data corresponding to the smallest unit of storage on a peripheral device. For disks, a physical record is a sector. POINTER The address or memory location of a block of data or a single data item. The address "points" to the data. PROLOGUE The three bytes at the beginning of a disk field which uniquely identify it from any other data on the track. PROM Programmable Read Only Memory. PROMs are usually used on controller cards associated with peripherals to hold the driver program which interfaces the device to applications programs. PROMPT An output string which lets the user know that input is expected. A "*" is the prompt character for the APPLE monitor. PROTECTED DISK A diskette whose format or content has been modified to prevent its being copied. Most retail software today is distributed on protected disks to prevent theft. PSEUDO-OPCODE A special assembly language opcode which does not translate into a machine instruction. A pseudo-opcode instructs the assembler to perform some function, such as skipping a page in an assembly listing or reserving data space in the output object code. RANDOM ACCESS Direct access. The capability to rapidly access any single piece of data on a storage medium without having to sequentially read all of its predecessors. RAM Random Access Memory. Computer memory which will allow storage and retrieval of values by address. RECAL Recalibrate the disk arm so that the read/write head is positioned over track zero. This is done by pulling the arm as far as it will go to the outside of the diskette until it hits a stop, producing a "clacking" sound. RECORD A collection of associated data items or fields. One or more records are usually associated with a file. Each record might correspond to an employee, for example. REGISTER A named temporary storage location in the central processor itself. The 6502 has 5 registers; the A, X, Y, S, and P registers. Registers are used by an assembly language program to access memory and perform arithmetic. RELEASE A version of a distributed piece of software. There have been several releases of DOS. RELOCATABLE The attribute of an object module file which contains a machine language program and the information necessary to make it run at any memory location. RETURN CODE A numeric value returned from a subroutine, indicating the success or failure of the operation attempted. A return code of zero usually means there were no errors. Any other value indicates the nature of the error, as defined by the design of the subroutine. ROM Read Only Memory. Memory which has a permanent value. The APPLE monitor and BASIC interpreters are stored in ROM. RWTS Read/Write Track/Sector. A collection of subroutines which allow access to the diskette at a track and sector level. RWTS is part of DOS and may be called by external assembly language programs. SEARCH The process of scanning a track for a given sector. SECTOR The smallest updatable unit of data on a disk track. One sector on an APPLE DISK II contains 256 data bytes. SECTOR ADDRESS A disk field which identifies the sector data field which follows in terms of its volume, track, and sector number. SECTOR DATA A disk field which contains the actual sector data in nibbilized form. SEEK The process of moving the disk arm to a given track. SELF-SYNC Also called "auto-sync" bytes. Special disk bytes which contain more than 8 bits, allowing synchronization of the hardware to byte boundaries when reading. SEQUENTIAL ACCESS A mode of data retreival where each byte of data is read in the order in which it was written to the disk. SERIAL As opposed to parallel. A communication mode which sends data bits one at a time over a single line or wire. SHIFT A logical operation which moves the bits of a byte either left or right one position, moving a 0 into the bit at the other end. SLAVE DISK A diskette with a copy of DOS which is not relocatable. The DOS image will always be loaded into the same memory location, regadless of the size of the machine. SOFT ERROR A recoverable I/O error. A worn diskette might produce soft errors occasionally. SOFTWARE Computer programs and data which can be loaded into RAM memory and executed. SOURCE CODE A program in a form which is understandable to humans; in character form as opposed to internal binary machine format. Source assembly code must be processed by an assembler to translate it into machine or "object" code. SKEWING The process of interleaving sectors. See INTERLEAVE. STATE MACHINE A process (in software or hardware) which defines a unique target state, given an input state and certain conditions. A state machine approach is used in DOS to keep track of its video intercepts and by the hardware on the disk controller card to process disk data. STROBE The act of triggering an I/O function by momentarily referencing a special I/O address. Strobing $C030 produces a click on the speaker. Also called "toggling". SUBROUTINE A program whose function is required repeatedly during execution, and therefore is called by a main program in several places. TABLE A collection of data entries, having similar format, residing in memory. Each entry might contain the name of a program and its address, for example. A "lookup" can be performed on such a table to locate any given program by name. TOGGLE The act of triggering an I/O function by momentarily referencing a special I/O address. Toggling $C030 produces a click on the speaker. Also called "strobe". TOKENS A method where human recognizable words may be coded to single binary byte values for memory compression and faster processing. BASIC statements are tokenized, where hex codes are assigned to words like IF, PRINT, and END. TRACK One complete circular path of magnetic storage on a diskette. There are 35 concentric tracks on an APPLE diskette. TRANSLATE TABLE A table of single byte codes which are to replace input codes on a one-for-one basis. A translate table is used to convert from 6 bit codes to disk codes. T/S LIST Track/Sector List. A sector which describes the location of a file by listing the track and sector number for each of its data sectors in the order that they are to be read or written. TTL Transistor to Transistor Logic. A standard for the interconnection of integrated circuits which also defines the which voltages represent 0's and 1's. UTILITY A program which is used to maintain, or assist in the development of, other programs or disk files. VECTOR A collection of pointers or JMP instructions at a fixed location in memory which allow access to a relocatable program or data. VOLUME An identification for a diskette, disk platter, or cassette, containing one or more files. VTOC Volume Table Of Contents. Based upon the IBM OS/VS VTOC. On the APPLE, a sector mapping the free sectors on the diskette and giving the location of the directory. WARMSTART A restart of a program which retains, as much as is possible, the work which was in progress at the time. A DOS warmstart retains the BASIC program in memory. WRITE PROTECTED A diskette whose write protect notch is covered, preventing the disk drive from writing on it. ZAP From the IBM utility program, SUPERZAP. A program which allows updates to a disk at a byte level, using hexadecimal. ZERO PAGE The first 256 bytes of memory in a 6502 based machine. Zero page locations have special significance to the central processor, making their management and assignment critical.