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