beneath-apple-dos/appendixC-2.txt

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.
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