A BRIEF OUTLINE OF CP/M AND CP/M COMMANDS
Eli Freedman
ABC Br, IBD
These notes are necessarily sketchy. Not every CP/M utility is
mentioned; of those that are, not every ramification is covered.
CP/M stands for Control Program for Microcomputers. It is a
collection of computer programs for the Intel 8080 and the Zilog
Z80 chips. CP/M handles all of the sometimes intricate and
always tedious details of input/output (I/O), including communi-
cation among processor, disks, console, and printer, including
disk-file maintenance.
For the North Star Advantage, CP/M is furnished on a 5-1/4 inch
floppy disk where the system occupies the first 3 tracks; these
are called the system tracks. When you press the red button on
the back of an Advantage and then the RETURN key, the CP/M system
is loaded into the computer. This operation is called "booting"
the computer; note that it is not done with the foot! When the
computer is booted, CP/M loads itself into the computer's core
memory. It occupies approximately 6000 (decimal) bytes at (or
near) the top of the memory, and also the first 256 (decimal)
bytes starting at 0.
There are two kinds of "booting":
Alternate How
Name Name Accomplished Why
----- -------- ------------- --------------------------
cold hard turn machine on start-up
press red button resume after crash
special program
warm soft press ^C read disk directory
After booting, the screen displays A>, meaning that you are
"logged in" on drive A. If you type B:, the screen shows B>,
meaning that the logged drive is now B. WordStar and many other
programs require that you know which drive is the logged one.
The principal components of CP/M are the Basic Input/Output
System (BIOS), the Basic Disk Operating System (BDOS), and the
Console Command Processor (CCP). These programs are all located
in the "high memory" part of CP/M. The largest amount of the
computer's random-access memory lies between the two parts of
CP/M and is referred to as the Transient Program Area (TPA). All
of the TPA is available to the user; some CP/M programs also use
it.
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CP/M has two kinds of commands, built-in and transient. The
built-in commands (ERA, TYPE, SAVE, REN, and DIR) are in the CCP,
and do not change anything in the TPA. Also, they do not show up
in the directory listing of the disk. The transient commands do
show up in the directory (unless you go to the extra trouble of
hiding them--it can be done) and they are loaded into the TPA for
execution.
FILE NAMES. Almost all CP/M commands work on file names. A file
name is 1 to 8 letters or numbers, plus an optional extension,
which is a period and 1 to 3 letters or numbers. Some special
characters can be used in file names. The drive letter may
appear in front of the name, followed by a colon. If the drive
letter is not used explicitly, the logged drive is assumed by
default.
Examples: MYFILE.EXT URFILE B:afile.for A:CPNOTES.TXT
Note that A:MYFILE is different from B:MYFILE; likewise,
MYFILE.TXT is not the same as MYFILE.BAK.
Certain extensions have special meanings:
.FOR A FORTRAN source file.
.BAS A BASIC language file.
.REL Relocatable code produced by various
compilers.
.ASM Assembly language source file.
.HEX The output from certain assemblers.
.PRN A print listing produced by some compilers.
.COM A command file (executable program).
.SUB A SUBMIT file (similar to a CCL procedure).
.BAK A backup file; produced by WordStar and some
other programs.
.MAC A file for the Microsoft M80 macro assembler.
These uses are required in most cases. For example: the Micro-
soft FORTRAN compiler will not compile a program without a .FOR
extension; you cannot execute a program that does not have a .COM
extension. I recommend that you use extensions only to designate
the kind of file; don't rely on the extension alone (except for
WILD-CARD DESIGNATORS. In many cases one wants to refer to a
class of files, not just one. This is done with the "wild-card
designators," * and ?. The ? matches any letter; the * means
"any."
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Examples:
*.FOR means any file with the extension FOR.
AB??????.* means any file whose name starts with AB and
has any extension.
AB??????.TXT means any file whose name starts with AB
and has extension TXT.
SOME SPECIAL CONTROL CODES. Control codes are generated by
holding down the key marked CNTRL (or CONTROL) while pressing
another. In text, the up arrow, ^, is used to designate the
CNTRL key. In CP/M, certain control codes have special meanings:
^C Interrupt a command or program (may not always
work); perform a "soft boot" (read the directory on each disk
drive).
^S Stop/start the screen display.
^P Start/stop the printer; when "on", any text that
appears on the screen will also be printed.
^X Erase command line, return to col. 1
BUILT-IN COMMANDS.
DIR [A:URFILE.EXT]
Display the directory for a file or a disk.
Examples: DIR
Shows the directory for the logged disk.
DIR B:
Shows the directory for disk B no matter which disk is the logged
one.
DIR A:*.COM
Shows the directory for all files on the disk on drive A that
have the extension COM.
DIR B:MYFILE.*
Shows the directory for all files on drive B that have the name
MYFILE, no matter what their extension is.
REN NEWFILE.EX2=OLDFILE.EXT1
Rename a file. The old file name is replaced by the new file name
in the directory; the contents of the file are not disturbed.
ERA FILENAME
Erase the name of the file from the directory. The contents of
the file are not disturbed, and can be retrieved by special
programs.
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Examples: ERA B:*.BAK
Erases on all files on drive B with the extension BAK.
ERA A:MYFILE.TXT
Erases only MYFILE.TXT on drive A.
ERA *.*
Careful! This command will erase on files on the logged disk.
SOME CP/M TRANSIENT PROGRAMS
All programs that run under CP/M have the extension .COM. The
program is executed by typing the name without the extension.
Generally either lower- or upper-case letters may be used, but
there are exceptions (e.g., in FORMAT).
STAT
Display size and attributes of a file or files or a disk; also,
change the designations of I/O units. STAT by itself merely
tells you how much space is left on the logged drive. STAT B:
tells you how much space is left on the disk on drive B:.
STAT A:*.* tells you the name of every file on the disk now on
drive A:, and its attributes. There are two attributes: R/W,
meaning both reading and writing are permitted; and R/O, meaning
the file is read-only.
STAT B:*.COM gives this information for every .COM file on drive
B:. STAT also permits you to change device assignments; see the
references.
COPY
Copy the contents of one disk onto another entirely, including
the system tracks. COPY is self-guiding; just type the command
and follow the instructions. Note that COPY refers to the drives
by number, not by letter.
FORMAT
A new disk cannot be used until it has been formatted. For CP/M
systems, this means that all of the tracks are filled with the
format character (E5 HEX). This is accomplished by typing FORMAT
and then following the directions that appear. A disk does not
have to be formatted if the very next thing you do to it is to
COPY something onto it, since this automatically initializes the
disk.
PIP
Copy one or more files to other files; the new files do not have
to be on the same drive, but they may be.
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Examples: PIP B:NEWFILE.EX2 = A:OLDFILE.EX1
PIP NEWFILE = B:OLDFILE
PIP A:*.* = B:*.* Copies every file from B: to A:;
the names remain the same, except for the change in drive
designation.
PIP B:=A:*.FOR Copies every FORTRAN file on drive A:
onto drive B:
PIP can be invoked alone; it then responds *. You then name
files two by two (i.e., new and old) for copying. Terminate with
a CR.
SUBMIT FILE.SUB PAR1 PAR2 PAR3 ...
A great program that permits you to operate in almost a batch
mode. The quantities PARi replace dummy arguments. You build up
a sequence of CP/M commands in a file whose extension must be
you place the dummy arguments, $1, $2, etc. When the file is
then submmitted, CP/M will make the substitutions, print the
command, and then execute it.
Example: Suppose you create a file TEST.SUB whose contents are
PIP $1:$2.TXT=B:$3.TXT
Then you type
SUBMIT TEST A GOOD BAD
The screen will show the complete command
PIP A:GOOD.TXT=B:BAD.TXT
and then the program will execute.
SAVE n FILENAME
This command transfers n*256 bytes from memory starting at 256
(decimal) to the named file on disk. It is used after working
with DDT (see references). Also, some communication packages
(e.g., CMOD) transfer data from an external computer to your
computer's memory; SAVE is then used to store the data on a disk.
SYSGEN
It is very convenient to be able to boot your computer from every
disk you use. This means that every disk must have a CP/M system
on it. (I also recommend that every disk have PIP, FORMAT, and
COPY on it.)
There are two ways in which you can put a CP/M saystem on a disk.
You can use COPY, which copies everything from one disk to
another, track for track. This method has the disadvantage that
you then have to remove all of the files that were also copied.
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SOME REFERENCES
In my opinion, the best reference on CP/M is:
Rodnay Zaks, "The CP/M Handbook," Sybex; 1980.
J. N. Fernandez & R. Ashley, "Using CP/M," John Wiley; 1980 is
written in a "programmed learning" style that I found
infuriating. It is a good self-teaching text, but a poor
reference book.
CP/M is a product of Digital Research. This company supplies
Manuals with the system when you buy it. They have a well-
deserved reputation for denseness and incomprehensibility.
An interesting book is
Jack D. Dennon, "CP/M Revealed," Hayden; 1982. It gives some of
the details of how CP/M does its stuff.
ACKNOWLEDGMENT
Many thanks to George E. Keller for invaluable assistance and
advice.
version 2.01/9-I-84
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