Appendix H

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.
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
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 This attribute is set if the file has been archived.
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.
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.
Program that translates assembly language into the binary machine code. Assembly language is simply a set of mnemonics used to designate the instruction set of the CPU. See ASM in Section 3 of this manual.
Copy of a disk or file made for safekeeping, or the creation of the duplicate disk or file.
Basic Disk Operating System
Basic Disk Operating System. The BDOS module of the CP/M operating systemprovides an interface for a user program to the operating. This interface is in the form of a set of function calls which may be made to the BDOS through calls to location 0005H in page zero. The user program specifies the number of the desired function in register C. User programs running under CP/M should use BDOS functions for all I/O operations to remain compatible with other CP/M systems and future releases. The BDOS normally resides in high memory directly below the BIOS.
Address value which when added to the origin address of your BIOS module produces lF80H, the address of the BIOS module in the MOVCPM image. There is also a bias value that when added to the BOOT module origin produces 0900H, the address of the BOOT module in the MOVCPM image. You mu'st use these bias values with the R command under DDT or SID" when you patch a CP/M system. If you do not, the patched system may fall to function.
Base 2 numbering system. A binary digit can have one of two values: 0 or 1. Binary numbers are used in computers because the hardware can most easily exhibit two states: off and on. Generally, a bit in memory represents one binary digit.
Basic Input/Output System
Basic Input/Output System. The BIOS is the only hardware-dependent module of the CP/M system. It provides the BDOS with a set of primitive I/O operations. The BIOS is an assembly language module usually written by the user, hardware manufacturer, or independent software vendor, and is the key to CP/M's portability. The BIOS interfaces the CP/M system to its hardware environment through a standardized jump table at the front of the BIOS routine and through a set of disk parameter tables which define the disk environment. Thus, the BIOS provides CP/M with a completely table-driven I/O system.
BIOS base
Lowest address of the BIOS module in memory, that by definition must be the first entry point in the BIOS jump table.
Switch in memory that can be set to on (1) or off (0). Bits are grouped into bytes, eight bits to a byte, which is the smallest directly addressable unit in an Intel 8080 or Zilog Z80.

By common convention, the bits in a byte are numbered from right, 0 for the low-order bit, to left, 7 for the high-order bit. Bit values are often represented in hexadecimal notation by grouping the bits from the low-order bit in groups of four. Each group of four bits can have a value from 0 to 15 and thus can easily be represented by one hexadecimal digit.

See block mask.
Basic unit of disk space allocation. Each disk drive has a fixed block size (BLS) defined in its disk parameter block in the BIOS. A block can consist of 1K, 2K, 4K, 8K, or 16K consecutive bytes. Blocks are numbered relative to zero so that each block is unique and has a byte displacement in a file equal to the block number times the block size.
block mask (BLM)
Byte value in the disk parameter block at DPB + 3. The block mask is always one less than the number of 128 byte sectors that are in one block. Note that BLM = (2 ** BSH) - 1.
block shift (BSH)
Byte parameter in the disk parameter block at DPB + 2. Block shift and block mask (BLM) values are determined by the block size (BLS). Note that BLM = (2 ** BSH) - 1.
blocking & deblocking algorithm
In some disk subsystems the disk sector size is larger than 128 bytes, usually 256, 512, 1024, or 2048 bytes. When the host sector size is larger than 128 bytes, host sectors must be buffered in memory and the 128-byte CP/M sectors must be blocked and deblocked by adding an additional module, the blocking and deblocking algorithm, between the BIOS disk I/O routines and the actual disk I/O. The host sector size must be an even multiple of 128 bytes for the algorithm to work correctly. The blocking and deblocking algorithm allows the BDOS and BIOS to function exactly as if the entire disk consisted only of 128-byte sectors, as in the standard CP/M installation.
Block size in bytes. See block.
Process of loading an operating system into memory. A boot program is a small piece of code that is automatically executed when you power-up or reset your computer. The boot program loads the rest of the operating system into memory in a manner similar to a person pulling himself up by his own bootstraps. This process is sometimes called a cold boot or cold start. Bootstrap pocedures vary from system to system. The boot program must be customized for the memory size and hardware environment that the operating system manages. Typically, the boot resides on the first sector of the system tracks on your system disk. When executed, the boot loads the remaining sectors of the system tracks into high memory at the location for which the CP/M system has been configured. Finally, the boot transfers execution to the boot entry point in the BIOS jump table so that the system can initialize itself. In this case, the boot program should be placed at 900H in the SYSGEN image. Alternatively, the boot program may be located in ROM.
See boot.
See block shift.
General purpose file access method that has become the standard organization for indexes in large data base systems. BTREE provides near optimum performance over the full range of file operations, such as insertion, deletion, search, and search next.
Area of memory that temporarily stores data during the transfer of information.
built-in commands
Commands that permanently reside in memory. They respond quickly because they are not accessed from a disk.
Unit of memory or disk storage containing eight bits. A byte can represent a binary number between 0 and 255, and is the smallest unit of memory that can be addressed directly in 8-bit CPUs such as the Intel 8080 or Zilog Z80.
Console Command Processor. The CCP is a module of the CP/M operating system. It is loaded directly below the BDOS module and interprets and executes commands typed by the console user. Usually these commands are programs that the CCP loads and calls. Upon completion, a command program may return control to the CCP if it has not overwritten it. If it has, the program can reload the CCP into memory by a warm boot operation initiated by either a jump to zero, BDOS system reset (Function 0), or a cold boot. Except for its location in high memory, the CCP works like any other standard CP/M program; that is, it makes only BDOS function calls for its I/O operations.
CCP base
Lowest address of the CCP module in memory. This term sometimes refers to the base of the CP/M system in memory, as the CCP is normally the lowest CP/M module in high memory.
checksum vector (CSV)
Contiguous data area in the BIOS, with one byte for each directory sector to be checked, that is, CKS bytes. See CKS. A checksum vector is initialized and maintained for each logged-in drive. Each directory access by the system results in a checksum calculation that is compared with the one in the checksum vector. If there is a discrepancy, the drive is set to Read-Only status. This feature prevents the user from inadvertently switching disks without logging in the new disk. If the new disk is not logged-in, it is treated the same as the old one, and data on it might be destroyed if writing is done.
Number of directory records to be checked summed on directory accesses. This is a parameter in the disk parameter block located in the BIOS. If the value of CKS is zero, then no directory records are checked. CKS is also a parameter in the diskdef macro library, where it is the actual number of directory elements to be checked rather than the number of directory records.
cold boot
See boot. Cold boot also refers to a jump to the boot entry. point in the BIOS jump table.
Filetype for a CP/M command file. See command file.
CP/M command line. In general, a CP/M command line has three parts: the command keyword, command tail, and a carriage return. To execute a command, enter a CP/M command line directly after the CP/M prompt at the console and press the carriage return or enter key.
command file
Executable program file of filetype COM. A command file is a machine language object module ready to be loaded and executed at the absolute address of 0100H. To execute a command file, enter its primary filename as the command keyword in a CP/M command line.
command keyword
Name that identifies a CP/M command, usually the primary filename of a file of type COM, or a built-in command. The command keyword precedes the command tail and the carriage return in the command line.
command syntax
Statement that defines the correct way to enter a command. The correct structure generally includes the command keyword, the command tail, and a carriage return. A syntax line usually contains symbols that you should replace with actual values when you enter the command.
command tail
Part of a command that follows the command keyword in the command line. The command tail can include a drive specification, a filename and filetype, and options or parameters. Some commands do not require a command tail.
Mnemonic that represents the CP/M console device. For example, the CP/M command PIP CON:=TEST.SUB displays the file TEST.SUB on the console device. The explanation of the STAT command tells how to assign the logical device CON: to various physical devices. See console.
Name of the PIP operation that copies two or more separate files into one new file in the specified sequence.
Execution of two processes or operations simultaneously.
BIOS entry point to a routine that reads a character from the console device.
BIOS entry point to a routine that sends a character to the console device.
Primary input/output device. The console consists of a listing device, such as a screen or teletype, and a keyboard through which the user communicates with the operating system or applications program.
Console Command Processor
See CCP.
BIOS entry point to a routine that returns the status of the console device.
control character
Nonprinting character combination. CP/M interprets some control characters as simple commands such as line editing functions. To enter a control character, hold down the CONTROL key and strike the specified character key.
Control Program for Microcomputers
See CP/M.
Control Program for Microcomputers. An operating system that manages computer resources and provides a standard systems interface to software written for a large variety of microprocessor-based computer systems.
CP/M 1.4 compatibility
For a CP/M 2 system to be able to read correctly single-density disks produced under a CP/M 1.4 system, the extent mask must be zero and the block size 1K. This is because under CP/M 2 an FCB may contain more than one extent. The number of extents that may be contained by an FCB is EXM + 1. The issue is of CP/M 1.4 compatibility also concerns random file I/O. To perform random file I/O under CP/M 1.4, you must maintain an FCB for each extent of the file. This scheme is upward compatible with CP/M 2 for files not exceeding 512K bytes, the largest file size supported under CP/M 1.4. If you wish to implement random I/O for files larger than 512K bytes under CP/M 2, you must use the random read and random write functions, BDOS functions 33, 34, and 36. In this case, only one FCB is used, and if CP/M 1.4 compatiblity is required, the program must use the return version number function, BDOS Function 12, to determine which method to employ.
CP/M prompt
Characters that indicate that CP/M is ready to execute your next command. The CP/M prompt consists of an upper- case letter, A-P, followed by a > character; for example, A>. The letter designates which drive is currently logged in as the default drive. CP/M will search this drive for the command file specified, unless the command is a built-in command or prefaced by a select drive command: for example, B:STAT.
Digital Research network operating system enabling microcomputers to obtain access to common resources via a network. CP/NET consists of MP/M masters and CP/M slaves with a network interface between them.
See checksum vector.
One-character symbol that can appear anywhere on the console screen. The cursor indicates the position where the next keystroke at the console will have an effect.
data file
File containing information that will be processed by a program.
See blocking & deblocking algorithm.
Currently selected disk drive and user number. Any command that does not specify a disk drive or a user number references the default disk drive and user number. When CP/M is first invoked, the default disk drive is drive A, and the default user number is 0.
default buffer
Default 128-byte buffer maintained at 0080H in page zero. When the CCP loads a COM file, this buffer is initialized to the command tall; that is, any characters typed after the COM file name are loaded into the buffer. The first byte at 0080H contains the length of the command tall, while the command tail itself begins at 0081H. The command tail is terminated by a byte containing a binary zero value. The I command under DDT and SID initializes this buffer in the same way as the CCP.
default FCB
Two default FCBs are maintained by the CCP at 005CH and 006CH in page zero. The first default FCB is initialized from the first delimited field in the command tail. The second default FCB is initialized from the next field in the command tail.
Special characters that separate different items in a command line; for example, a colon separates the drive specification from the filename. The CCP recognizes the following characters as delimiters: . : = ; < > - , blank, and carriage return. Several CP/M commands also treat the following as delimiter characters: , [ ] ( ) $. It is advisable to avoid the use of delimiter characters and lower-case characters in CP/M filenames.
Parameter in the diskdef macro library that specifies the number of directory elements on the drive.
DIR attribute
File attribute. A file with the DIR attribute can be displayed by a DIR command. The file can be accessed from the default user number and drive only.
128-byte scratchpad area for directory operations, usually located at the end of the BIOS. DIRBUF is used by the BDOS during its directory operations. DIRBUF also refers to the two-byte address of this scratchpad buffer in the disk parameter header at DPbase + 8 bytes.
Portion of a disk that contains entries for each file on the disk. In response to the DIR command, CP/M displays the filenames stored in the directory. The directory also contains the locations of the blocks allocated to the files. Each file directory element is in the form of a 32-byte FCB, although one file can have several elements, depending on its size. The maximum number of directory elements supported is specified by the drive's disk parameter block value for DRM.
directory element
Data structure. Each file on a disk has one or more 32-byte directory elements associated with it. There are four directory elements per directory sector. Directory elements can also be referred to as directory FCBs.
directory entry
File entry displayed by the DIR command. Sometimes this term refers to a physical directory element.
disk, diskette
Magnetic media used for mass storage in a computer system. Programs and data are recorded on the disk in the same way music can be recorded on cassette tape. The CP/M operating system must be initially loaded from disk when the computer is turned on. Diskette refers to smaller capacity removable floppy diskettes, while disk may refer to either a diskette, removable cartridge disk, or fixed hard disk. Hard disk capacities range from five to several hundred megabytes of storage.
diskdef macro library
Library of code that when used with MAC, the Digital Research macro assembler, creates disk definition tables such as the DPB and DPH automatically.
disk drive
Peripheral device that reads and writes information on disk. CP/M assigns a letter to each drive under its control. For example, CP/M may refer to the drives in a four-drive system as A, B, C, and D.
disk parameter block (DPB)
Data structure referenced by one or more disk parameter headers. The disk parameter block defines disk characteristics in the fields listed below:

The address of the disk parameter block is located in the disk parameter header at DPbase + 0AH. CP/M Function 31 returns the DPB address. Drives with the same characteristics can use the same disk parameter header, and thus the same DPB. However, drives with different characteristics must each have their own disk parameter header and disk parameter blocks. When the BDOS calls the SELDSK entry point in the BIOS, SELDSK must return the address of the drive's disk parameter header in register HL.

disk parameter header (DPH)
Data structure that contains information about the disk drive and provides a scratchpad area for certain BDOS operations. The disk parameter header contains six bytes of scratchpad area for the BDOS, and the following five 2-byte parameters:

Given n disk drives, the disk parameter headers are arranged in a table whose first row of 16 bytes corresponds to drive 0, with the last row corresponding to drive n - 1.

Parameter in the diskdef macro library specifying the number of data blocks on the drive.
Direct Memory Access. DMA is a method of transferring data from the disk into memory directly. In a CP/M system, the BDOS calls the BIOS entry point READ to read a sector from the disk into the currently selected DMA address. The DMA address must be the address of a 128-byte buffer in memory, either the default buffer at 0080H in page zero, or a user-assigned buffer in the TPA. Similarly, the BDOS calls the BIOS entry point WRITE to write the record at the current DMA address to the disk.
Parameter in the diskdef macro library specifying the logical drive number.
See disk parameter block.
See disk parameter header.
2-byte parameter in the disk parameter block at DPB + 7. DRM is one less than the total number of directory entries allowed for the drive. This value is related to DPB bytes AL0 and AL1, which allocates up to 16 blocks for directory entries.
2-byte parameter of the disk parameter block at DPB + 5. DSM is the maximum data block number supported by the drive. The product BLS times (DSM + 1) is the total number of bytes held by the drive. This must not exceed the capacity of the physical disk less the reserved system tracks.
Utility program that creates and modifies text files. An editor can be used for creation of documents or creation of code for computer programs. The CP/M editor is invoked by typing the command ED next to the system prompt on the console.
Extent number field in an FCB. See extent.
Ready to be run by the computer. Executable code is a series of instructions that can be carried out by the computer. For example, the computer cannot execute names and addresses, but it can execute a program that prints all those names and addresses on mailing labels.
execute a program
Start the processing of executable code.
See extent mask.
16K consecutive bytes in a file. Extents are numbered from 0 to 31. One extent can contain 1, 2, 4, 8, or 16 blocks. EX is the extent number field of an FCB and is a one-byte field at FCB + 12, where FCB labels the first byte in the FCB. Depending on the block size (BLS) and the maximum data block number (DSM), an FCB can contain 1, 2, 4, 8, or 16 extents. The EX field is normally set to 0 by the user but contains the current extent number during file I/O. The term FCB folding describes FCBs containing more than one extent. In CP/M version 1.4, each FCB contained only one extent. Users attempting to perform random record I/O and maintain CP/M 1.4 compatiblity should be aware of the implications of this difference. See CP/M 1.4 compatibility.
extent mask (EXM)
A byte parameter in the disk parameter block located at DPB + 3. The value of EXM is determined by the block size (BLS) and whether the maximum data block number (DSM) exceeds 255. There are EXM + 1 extents per directory FCB.
See File Control Block.
Collection of characters, instructions, or data that can be referenced by a unique identifier. Files are usually stored on various types of media, such as disk, or magnetic tape. A CP/M file is identified by a file specification and resides on disk as a collection of from zero to 65,536 records. Each record is 128 bytes and can contain either binary or ASCII data. Binary files contain bytes of data that can vary in value from 0H to 0FFH. ASCII files contain sequences of character codes delineated by a carriage return and line-feed combination; normally byte values range from 0H to 7FH. The directory maps the file as a series of physical blocks. Although files are defined as a sequence of consecutive logical records, these records can not reside in consecutive sectors on the disk. See also block, directory, extent, record, and sector.
File Control Block (FCB)
Structure used for accessing files on disk. Contains the drive, filename, filetype, and other information describing a file to be accessed or created on the disk. A file control block consists of 36 consecutive bytes specified by the user for file I/O functions. FCB can also refer to a directory element in the directory portion of the allocated disk space. These contain the same first 32 bytes of the FCB, but lack the current record and random record number bytes.
Name assigned to a file. A filename can include a primary filename of one to eight characters; a filetype of zero to three characters. A period separates the primary filename from the filetype.
file specification
Unique file identifier. A complete CP/M file specification includes a disk drive specification followed by a colon, d:, a primary filename of one to eight characters, a period, and a filetype of zero to three characters. For example, b:example.tex is a complete CP/M file specification.
Extension to a filename. A filetype can be from zero to three characters and must be separated from the primary filename by a period. A filetype can tell something about the file. Some programs require that files to be processed have specific filetypes.
floppy disk
Flexible magnetic disk used to store information. Floppy disks come in 5 1/4- and 8-inch diameters.
Parameter in the diskdef macro library specifying the first physical sector number. This parameter is used to determine SPT and build XLT.
hard disk
Rigid, platter-like, magnetic disk sealed in a container. A hard disk stores more information than a floppy disk.
Physical components of a computer.
hexadecimal notation
Notation for base 16 values using the decimal digits and letters A, B, C, D, E, and F to represent the 16 digits. Hexadecimal notation is often used to refer to binary numbers. A binary number can be easily expressed as a hexadecimal value by taking the bits in groups of 4, starting with the least significant bit, and expressing each group as a hexadecimal digit, 0-F. Thus the bit value 1011 becomes 0BH and 10110101 becomes 0B5H.
hex file
ASCII-printable representation of a command, machine language, file.
hex file format
Absolute output of ASM and MAC for the Intel 8080 is a hex format file, containing a sequence of absolute records that give a load address and byte values to be stored, starting at the load address.
BIOS entry point which sets the disk head of the currently selected drive to the track zero position.
Physical characteristics of a hard disk drive in a system using the blocking and deblocking algorithm. The term, host, helps distinguish physical hardware characteristics from CP/M's logical characteristics. For example, CP/M sectors are always 128 bytes, although the host sector size can be a multiple of 128 bytes.
Data going into the computer, usually from an operator typing at the terminal or by a program reading from the disk.
See I/O.
Object that allows two independent systems to communicate with each other, as an interface between hardware and software in a microcomputer.
Abbreviation for input/output. Usually refers to input/output operations or routines handling the input and output of data in the computer system.
A one-byte field in page zero, currently at location 0003H, that can support a logical-to-physical device mapping for I/O. However, its implementation in your BIOS is purely optional and might or might not be supported in a given CP/M system. The IOBYTE is easily set using the command:
STAT <logical device> = <physical device>

The CP/M logical devices are CON:, RDR:, PUN:, and LST:; each of these can be assigned to one of four physical devices. The IOBYTE can be initialized by the BOOT entry point of the BIOS and interpreted by the BIOS I/O entry points CONST, CONIN, CONOUT, LIST, PUNCH, and READER. Depending on the setting of the IOBYTE, different I/O drivers can be selected by the BIOS. For example, setting LST:=TTY: might cause LIST output to be directed to a serial port, while setting LST:=LPT: causes LIST output to be directed to a parallel port.

Abbreviation for kilobyte. See kilobyte.
See command keyword.
kilobyte (K)
1024 bytes or 0400H bytes of memory. This is a standard unit of memory. For example, the Intel 8080 supports up to 64K of memory address space or 65,536 bytes. 1024 kilobytes equal one megabyte, or over one million bytes.
Utility program used to combine relocatable object modules into an absolute file ready for execution. For example, LINK-80(TM) creates either a COM or PRL file from relocatable REL files, such as those produced by PL/1-80(TM).
A BIOS entry point to a routine that sends a character to the list device, usually a printer.
list device
Device such as a printer onto which data can be listed or printed.
BIOS entry point to a routine that returns the ready status of the list device.
Utility program that brings an absolute program image into memory ready for execution under the operating system, or a utility used to make such an image. For example, LOAD prepares an absolute COM file from the assembler hex file output that is ready to be executed under CP/M.
logged in
Made known to the operating system, in reference to drives. A drive is logged in when it is selected by the user or an executing process. It remains selected or logged in until you change disks in a floppy disk drive or enter CTRL-C at the command level, or until a BDOS Function 0 is executed.
Representation of something that might or might not be the same in its actual physical form. For example, a hard disk can occupy one physical drive, yet you can divide the available storage on it to appear to the user as if it were in several different drives. These apparent drives are the logical drives.
logical sector
See sector.
logical-to-physical sector translation table
See XLT.
Diskdef macro library parameter specifying the last physical sector number.
Logical CP/M list device, usually a printer. The CP/M list device is an output-only device referenced through the LIST and LISTST entry points of the BIOS. The STAT command allows assignment of LST: to one of the physical devices: TTY:, CRT:, LPT:, or UL1:, provided these devices and the IOBYTE are implemented in the LIST and LISTST entry points of your CP/M BIOS module. The CP/NET command NETWORK allows assignment of LST: to a list device on a network master. For example, PIP LST:=TEST.SUB prints the file TEST.SUB on the list device.
macro assembler
Assembler code translator providing macro processing facilities. Macro definitions allow groups of instructions to be stored and substituted in the source program as the macro names are encountered. Definitions and invocations can be nested and macro parameters can be formed to pass arbitrary strings of text to a specific macro for substitution during expansion.
Over one million bytes; 1024 kilobytes. See byte, and kilobyte.
Silicon chip that is the central processing unit microprocessor: microprocessor: (CPU) of the microcomputer. The Intel 8080 and the Zilog Z80 are microprocessors commonly used in CP/M systems.
MOVCPM image
Memory image of the CP/M system created by MOVCPM. This image can be saved as a disk file using the SAVE command or placed on the system tracks using the SYSGEN command without specifying a source drive. This image varies, depending on the presence of a one-sector or two-sector boot. If the boot is less than 128 bytes (one sector), the boot begins at 0900H, the CP/M system at 0980H, and the BIOS at 1F80H. Otherwise, the boot is at 0900H, the CP/M system at 1000H, and the BIOS at 2000H. In a CP/M 1.4 system with a one-sector boot, the addresses are the same as for the CP/M 2 system-except that the BIOS begins at 1E80H instead of 1F80H.
Multi-Programming Monitor control program. A microcomputer operating system supporting multi-terminal access with multi- programming at each terminal.
The capability of initiating and executing more than one program at a time. These programs, usually called processes, are time-shared, each receiving a slice of CPU time on a round-robin basis. See concurrency.
One half of a byte, usually the high-order or low-order 4 bits in a byte.
Two-byte parameter in the disk parameter block at DPB + 13 bytes. This value specifies the number of reserved system tracks. The disk directory begins in the first sector of track OFF.
Diskdef macro library parameter specifying the number of reserved system tracks. See OFF.
operating system
Collection of programs that supervises the execution of other programs and the management of computer resources. An operating system provides an orderly input/output environment between the computer and its peripheral devices. It enables user-written programs to execute safely. An operating system standardizes the use of computer resources for the programs running under it.
One of many parameters that can be part of a command tall. Use options to specify additional conditions for a command's execution.
Data that is sent to the console, disk, or printer.
256 consecutive bytes in memory beginning on a page boundary, whose base address is a multiple of 256 (100H) bytes. In hex notation, pages always begin at an address with a least significant byte of zero.
page relocatable program
See PRL.
page zero
Memory region between 0000H and 0100H used to hold critical system parameters. Page zero functions primarily as an interface region between user programs and the CP/M BDOS module. Note that in non-standard systems this region is the base page of the system and represents the first 256 bytes of memory used by the CP/M system and user programs running under it.
Value in the command tail that provides additional information for the command. Technically, a parameter is a required element of a command.
peripheral devices
Devices external to the CPU. For example, terminals, printers, and disk drives are common peripheral devices that are not part of the processor but are used in conjunction with it.
Characteristic of computer components, generally hardware, that actually exist. In programs, physical components can be represented by logical components.
primary filename
First 8 characters of a filename. The primary filename is a unique name that helps the user identify the file contents. A primary filename contains one to eight characters and can include any letter or number and some special characters. The primary filename follows the optional drive specification and precedes the optional filetype.
Page relocatable program. A page relocatable program is stored on disk with a PRL filetype. Page relocatable programs are easily relocated to any page boundary and thus are suitable for execution in a nonbanked MP/M system.
Series of coded Instructions that performs specific tasks when executed by a computer. A program can be written in a processor-specific language or a high-level language that can be implemented on a number of different processors.
Any characters displayed on the video screen to help the user decide what the next appropriate action is. A system prompt is a special prompt displayed by the operating system. The alphabetic character indicates the default drive. Some applications programs have their own special prompts. See CP/M prompt.
Logical CP/M punch device. The punch device is an output-only device accessed through the PUNCH entry point of the BIOS. In certain implementations, PUN: can be a serial device such as a modem.
BIOS entry point to a routine that sends a character to the punch device.
Logical CP/M reader device. The reader device is an input-only device accessed through the READER entry point in the BIOS. See PUN:.
Entry point in the BIOS to a routine that reads 128 bytes from the currently selected drive, track, and sector into the current DMA address.
Entry point to a routine in the BIOS that reads the next character from the currently assigned reader device.
Read-Only (R/O)
Attribute that can be assigned to a disk file or a disk drive. When assigned to a file, the Read-Only attribute allows you to read from that file but not write to it. When assigned to a drive, the Read-Only attribute allows you to read any file on the disk, but prevents you from adding a new file, erasing or changing a file, renaming a file, or writing on the disk. The STAT command can set a file or a drive to Read-Only. Every file and drive is either Read-Only or Read-Write. The default setting for drives and files is Read-Write, but an error in resetting the disk or changing media automatically sets the drive to Read-Only until the error is corrected. See also ROM.
Read-Write (R/W)
Attribute that can be assigned to a disk file or a disk drive. The Read-Write attribute allows you to read from and write to a specific Read-Write file or to any file on a disk that is in a drive set to Read-Write. A file or drive can be set to either Read-Only or Read-Write.
Group of bytes in a file. A physical record consists of 128 bytes and is the basic unit of data transfer between the operating system and the application program. A logical record might vary in length and is used to represent a unit of information. Two 64-byte employee records can be stored in one 128-byte physical record. Records are grouped together to form a file.
recursive procedure
Code that can call itself during execution.
reentrant procedure
Code that can be called by one process while another is already executing it. Thus, reentrant code can be shared between different users. Reentrant procedures must not be self-modifying; that is, they must be pure code and not contain data. The data for reentrant procedures can be kept in a separate data area or placed on the stack.
restart (RST)
One-byte call instruction usually used during interrupt sequences and for debugger break pointing. There are eight restart locations, RST 0 through RST 7, whose addresses are given by the product of 8 times the restart number.
See Read-Only.
Read-Only memory. This memory can be read but not written and so is suitable for code and preinitialized data areas only.
See restart.
See Read-Write.
In a CP/M system, a sector is always 128 consecutive bytes. A sector is the basic unit of data read and written on the disk by the BIOS. A sector can be one 128-byte record in a file or a sector of the directory. The BDOS always requests a logical sector number between 0 and (SPT-1). This is typically translated into a physical sector by the BIOS entry point SECTRAN. In some disk subsystems, the disk sector size is larger than 128 bytes, usually a power of two, such as 256, 512, 1024, or 2048 bytes.

These disk sectors are always referred to as host sectors in CP/M documentation and should not be confused with other references to sectors, in which cases the CP/M 128-byte sectors should be assumed. When the host sector size is larger than 128 bytes, host sectors must be buffered in memory and the 128-byte CP/M sectors must be blocked and deblocked from them. This can be done by adding an additional module, the blocking and deblocking algorithm, between the BIOS disk I/O routines and the actual disk I/O.

sectors per track (SPT)
A two-byte parameter in the disk parameter block at DPB + 0. The BDOS makes calls to the BIOS entry point SECTRAN with logical sector numbers ranging between 0 and (SPT - 1) in register BC.
Entry point to a routine in the BIOS that performs logical-to-physical sector translation for the BDOS.
Entry point to a routine in the BIOS that sets the currently selected drive.
Entry point to a routine in the BIOS that sets the currently selected DMA address. The DMA address is the address of a 128-byte buffer region in memory that is used to transfer data to and from the disk in subsequent reads and writes.
Entry point to a routine in the BIOS that sets the currently selected sector.
Entry point to a routine in the BIOS that sets the currently selected track.
skew factor
Factor that defines the logical-to-physical sector number translation in XLT. Logical sector numbers are used by the BDOS and range between 0 and (SPT - 1). Data is written in consecutive logical 128-byte sectors grouped in data blocks. The number of sectors per block is given by BLS/128. Physical sectors on the disk media are also numbered consecutively. If the physical sector size is also 128 bytes, a one-to-one relationship exists between logical and physical sectors. The logical-to- physical translation table (XLT) maps this relationship, and a skew factor is typically used in generating the table entries. For instance, if the skew factor is 6, XLT will be:



The skew factor allows time for program processing without missing the next sector. Otherwise, the system must wait for an entire disk revolution before reading the next logical sector. The skew factor can be varied, depending on hardware speed and application processing overhead. Note that no sector translation is done when the physical sectors are larger than 128 bytes, as sector deblocking is done in this case. See also sector, SKF, and XLT.

A diskdef macro library parameter specifying the skew factor to be used in building XLT. If SKF is zero, no translation table is generated and the XLT byte in the DPH will be 0000H.
Programs that contain machine-readable instructions, as opposed to hard-ware, which is the actual physical components of a computer.
source file
ASCII text file usually created with an editor that is an input file to a system program, such as a language translator or text formatter.
Stack pointer. See stack.
Process of accumulating printer output in a file while the printer is busy. The file is printed when the printer becomes free; a program does not have to wait for the slow printing process.
See sectors per track.
Reserved area of memory where the processor saves the return address when a call instruction is received. When a return instruction is encountered, the processor restores the current address on the stack to the program counter. Data such as the contents of the registers can also be saved on the stack. The push instruction places data on the stack and the pop instruction removes it. An item is pushed onto the stack by decrementing the stack pointer (SP) by 2 and writing the item at the SP address. In other words, the stack grows downward in memory.
Format for entering a given command.
See system attribute.
SYSGEN image
Memory image of the CP/M system created by SYSGEN when a destination drive is not specified. This is the same as the MOVCPM image that can be read by SYSGEN if a source drive is not specified. See MOVCPM image.
system attribute (SYS)
File attribute. You can give a file the system attribute by using the SYS option in the STAT command or by using the set file attributes function, BDOS Function 12. A file with the SYS attribute is not displayed in response to a DIR command. If you give a file with user number 0 the SYS attribute, you can read and execute that file from any user number on the same drive. Use this feature to make your commonly used programs available under any user number.
system prompt
Symbol displayed by the operating system indicating that the system is ready to receive input. See prompt and CP/M prompt.
system tracks
Tracks reserved on the disk for the CP/M system. The number of system tracks is specified by the parameter OFF in the disk parameter block (DPB). The system tracks for a drive always precede its data tracks. The command SYSGEN copies the CP/M system from the system tracks to memory, and vice versa. The standard SYSGEN utility copies 26 sectors from track 0 and 26 sectors from track 1. When the system tracks contain additional sectors or tracks to be copied, a customized SYSGEN must be used.
See console.
Transient Program Area. Area in memory where user programs run and store data. This area is a region of memory beginning at 0100H and extending to the base of the CP/M system in high memory. The first module of the CP/M system is the CCP, which can be overwritten by a user program. If so, the TPA is extended to the base of the CP/M BDOS module. If the CCP is overwritten, the user program must terminate with either a system reset (Function 0) call or a jump to location zero in page zero. The address of the base of the CP/M BDOS is stored in location 0006H in page zero least significant byte first.
Data on the disk media is accessed by combination of track and sector numbers. Tracks form concentric rings on the disk; the standard IBM single-density disks have 77 tracks. Each track consists of a fixed number of numbered sectors. Tracks are numbered from zero to one less than the number of tracks on the disk.
Transient Program Area
See TPA.
upward compatible
Term meaning that a program created for the previously released operating system, or compiler, runs under the newly released version of the same operating system.
Term used in CP/M and MP/M systems to distinguish distinct regions of the directory.
user number
Number assigned to files in the disk directory so that different users need only deal with their own files and have their own directories, even though they are all working from the same disk. In CP/M, files can be divided into 16 user groups.
Tool. Program that enables the user to perform certain operations, such as copying files, erasing files, and editing files. The utilities are created for the convenience of programmers and users.
Location in memory. An entry point into the operating system used for making system calls or interrupt handling.
warm start
Program termination by a jump to the warm start vector at location 0000H, a system reset (BDOS Function 0), or a CTRL-C typed at the keyboard. A warm start reinitializes the disk subsystem and returns control to the CP/M operating system at the CCP level. The warm start vector is simply a jump to the WBOOT entry point in the BIOS.
Entry point to a routine in the BIOS used when a warm start occurs. A warm start is performed when a user program branches to location 0000H, when the CPU is reset from the front panel, or when the user types CTRL-C. The CCP and BDOS are reloaded from the system tracks of drive A.
wildcard characters
Special characters that match certain specified items. In CP/M there are two wildcard characters: ? and *. The ? can be substituted for any single character in a filename, and the * can be substituted for the primary filename, the filetype, or both. By placing wildcard characters in filenames, the user creates an ambiguous filename and can quickly reference one or more files.
16-bit or two-byte value, such as an address value. Although the Intel 8080 is an 8-bit CPU, addresses occupy two bytes and are called word values.
Entry point to a routine in the BIOS that writes the record at the currently selected DMA address to the currently selected drive, track, and sector.
Logical-to-physical sector translation table located in the BIOS. SECTRAN uses XLT to perform logical-to-physical sector number translation. XLT also refers to the two-byte address in the disk parameter header at DPBASE + 0. If this parameter is zero, no sector translation takes place. Otherwise this parameter is the address of the translation table.
See page zero.

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