System information

Appendix H
Glossary
address: Number representing the location of a byte in memory. Within CP/M there are two
kinds of addresses: logical and physical. A physical address refers to an absolute and unique
location within the computer's memory space. A logical address refers to the offset or
displacement of a byte in relation to a base location. A standard CP/M program is loaded at
address 0100H, the base value; the first instruction of a program has a physical address of 0100H
and a relative address or offset of 0H.
allocation vector (ALV): An allocation vector is maintained in the BIOS for each logged-in disk
drive. A vector consists of a string of bits, one for each block on the drive. The bit corresponding
to a particular block is set to one when the block has been allocated and to zero otherwise. The
first two bytes of this vector are initialized with the bytes AL0 and AL1 on, thus allocating the
directory blocks. CP/M Function 27 returns the allocation vector address.
AL0, AL1: Two bytes in the disk parameter block that reserve data blocks for the directory.
These two bytes are copied into the first two bytes of the allocation vector when a drive is logged
in. See allocation vector.
ALV: See allocation vector.
ambiguous filename: Filename that contains either of the CP/M wildcard characters, ? or *, in
the primary filename, filetype, or both. When you replace characters in a filename with these
wildcard characters, you create an ambiguous filename and can easily reference more than one
CP/M file in a single command line.
American Standard Code for Information Interchange: See ASCII.
applications program: Program designed to solve a specific problem. Typical applications
programs are business accounting packages, word processing (editing) programs and mailing list
programs.
archive attribute: File attribute controlled by the high-order bit of the t3 byte (FCB + 11) in a
directory element. This attribute is set if the file has been archived.
argument: Symbol, usually a letter, indicating a place into which you can substitute a number,
letter, or name to give an appropriate meaning to the formula in question.
ASCII: American Standard Code for Information Interchange. ASCII is a standard set of
seven-bit numeric character codes used to represent characters in memory. Each character
requires one byte of memory with the high-order bit usually set to zero. Characters can be
numbers, letters, and symbols. An ASCII file can be intelligibly displayed on the video screen or
printed on paper.
Appendix G : Blocking and Deblocking Algorithms CP/M Operating System Manual
H-1