CP/M AT THE A> PROMPT
A small tour of CP/M 2.2

Start with a working boot disk or a copy of a known-good disk image.
Keep the original aside. The examples use an imaginary README.TXT;
substitute a real text filename from your disk. These examples show
how to list files, find them on another drive or user area, and run a
program.

1. Read the directory

A> means that A is the current drive and CP/M is waiting for a
command. Type only what follows the prompt, then press Return. [1]

    A>DIR
    A>DIR *.TXT
    A>TYPE README.TXT

DIR lists filenames; *.TXT selects the TXT filetype. TYPE displays one
ASCII text file. To pause scrolling, press CTRL-S; the standard 2.2
console resumes when you press another key. CTRL-U discards an
unfinished command line. [1]

A filename has up to eight characters, followed by an optional
filetype of up to three characters. README.TXT fits; a long modern
filename will need a shorter name before it belongs here. [2]

Use DIR *.ASM to look for assembly source files.

2. Visit another drive

Use these only if your system actually has a working B drive:

    A>DIR B:
    A>TYPE B:README.TXT
    A>B:
    B>DIR
    B>A:

A drive prefix targets that command's file operation. Entering B: on
its own changes the current drive; A: returns to A. [1]

Treat switching drive letters and physically exchanging disks as
separate jobs. A changed disk can trigger a read-only error if CP/M
has not been told about the change. Follow the machine's disk-change
procedure before doing any writing. A "Select" error means the
requested drive does not exist; "Bad Sector" can have several causes,
including missing media, formatting, or hardware. [3]

The explicit prefix is handy when you want to stay on A while reading
material from B. Switching to B is more convenient when several
successive commands will use it. Read the prompt after a drive change:
it gives you a quick check of where an unprefixed filename will be
sought.

3. Check the user area

    A>USER 1
    A>DIR
    A>USER 0

USER selects an area numbered 0 through 15; a cold start selects 0.
[1] The active user number helps select which directory entries file
operations see. A file's location therefore includes its drive and
user area, as well as its name. Changing the active user number does
not move the file. [2]

Try DIR before and after USER 1, then return with USER 0. A useful
catalogue entry would say "README.TXT on B, user 1", keeping both
parts of its location together.

4. Understand what is being run

DIR and TYPE are built into the command processor. For a program name
that is not built in, the standard processor looks for a COM file on
the addressed disk and loads it into memory. Typing a program's name
without .COM is how you invoke it. [2]

For example, STAT.COM is a separate utility. If it is available,
typing STAT USR: reports the active user number and the user areas
containing files on the current disk. That makes it a useful next step
after trying USER and DIR. [1]

"Transient" describes the way the program is loaded for execution; it
is still an ordinary file you can see in a directory listing. The
command processor supplies the .COM filetype when looking for the
program. [2]

The CCP interprets your commands. The BDOS provides operating-system
services, including file access. The BIOS supplies the low-level
hardware operations. These layers explain why CP/M manuals can
describe common commands while a computer's own handbook still matters
for its drives and console. [4]

5. Keep the version beside the instructions

CP/M Plus, also called CP/M 3, has features outside this 2.2 tour. Its
DIRSYS command lists system-marked files, and its extended DIR accepts
options such as USER=ALL. Those are not stock 2.2 command forms. CP/M
3 also distinguishes its built-in DIR from the transient utility
needed for extended options. [5]

Keep the operating-system version beside any commands you save for
later. A small notebook of working examples quickly becomes more
useful than a long command list: include the command, the drive and
user area, and what you used it to find.

REFERENCES

[1] Digital Research, CP/M Operating System Manual, section 1,
    especially 1.2-1.5. Web transcription, readable mirror:
https://ftpmirror.infania.net/sites/www.gaby.de/cpm/manuals/archive/cpm22htm/ch1.htm

[2] Same manual, section 5, especially 5.1-5.2 and functions 15,
    17 and 32. Web transcription, readable mirror:
https://ftpmirror.infania.net/sites/www.gaby.de/cpm/manuals/archive/cpm22htm/ch5.htm

[3] Same manual, appendix I, CP/M Error Messages. Web:
https://www.cpm.z80.de/manuals/archive/cpm22htm/axi.htm

[4] Same manual, appendix H, Glossary; CCP, BDOS and BIOS. Web:
https://www.cpm.z80.de/manuals/archive/cpm22htm/axh.htm

[5] Digital Research, CP/M 3 User's Guide, DIR command,
    printed pages 5-19 onward. PDF:
https://www.cpm.z80.de/manuals/cpm3-usr.pdf

Original CP/M 2.2 manual index. Web:
https://www.cpm.z80.de/manuals/archive/cpm22htm/index.htm