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1993-08-08
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MS-DOS E m u l a t o r f o r CP/M +
DEMO version
User's Manual
Nichita Sandru
Copyright (c) SanDES, 1990
- 2 -
1. Introduction
The MS-DOS Emulator is a program which allows the user to
handle files on MS-DOS disks under the control of CP/M Plus.
CP/M commands like DIR, ERA, etc. may be used with MS-DOS
disks exactly as with CP/M disks.
The MS-DOS Emulator cannot run MS-DOS programs because
they need an Intel 8086/88 family processor. They cannot run
on a Z80.
The MS-DOS Emulator automatically recognizes MS-DOS disks,
when they are inserted into the disk drive.
The emulator can only be used on a banked CP/M system. It
takes about 8 Kbytes in RAM bank 0 and 4 Kbytes in common RAM.
It can serve up to 16 disk drives, 5.25" (40 tracks) and 3.5"
formats.
This demo version is public domain. It contains a subset
of the capabilities of the commercial version. It may be
freely copied and distributed, together with this manual, but
altering the program or the manual is not permitted. The demo
version of the emulator may not be sold for profit. Only the
cost of materials, copying and postage may be asked.
The DEMO version consists of the following files:
- MSDOS.DOC - This user's manual.
- MSDOS.COM - The emulator.
2. The MS-DOS Format
An MS-DOS disk has 4 areas:
- The BOOT sector - 1'st sector on track 0 -
containing a program which loads the MS-DOS and
starts it (on a PC compatible), together with
information about the disk format.
- The FAT ("File Allocation Table") area containing a
"map" of the disk, showing the sectors occupied by
the files in the Data area.
- The DIR ("DIRectory") area containing a directory
of the files on the disk. Each file has an entry in
this directory, containing a description of the file.
The MS-DOS Emulator designates the DIR area as a
directory file with the name "\".
- 3 -
- The Data area containing the files.
Two kinds of files can be found on an MS-DOS disk: Data
files and directory files. The data files contain text,
programs etc. A directory file has the same structure as the
DIR area and it can contain entries for other directory files.
A directory file always contains two entries:
- An entry with the name ".", describing the
directory file itself;
- An entry with the name "..", designating the
directory where the directory file is listed. This
directory may be the DIR area or another directory
file.
The directory files form a tree structure, with the "\"
directory as root. The path to a directory is called "path".
The following MS-DOS formats are recognized by the MS-
DOS Emulator:
- 5.25" 160 Kbytes, SS.
- 5.25" 180 Kbytes, SS.
- 5.25" 320 Kbytes, DS.
- 5.25" 360 Kbytes, DS. (Standard PC/XT);
- 3.5" 720 Kbytes (PC/AT).
3. The CP/M Format
A CP/M disk has 3 areas:
- The system area (the first 0 ... 3 tracks);
- The DIR area containing file descriptions. The
large files are split into several areas ("extents"),
each with its own entry in the directory. These files
use several entries in the directory.
- The data area, divided into 16 "user" areas. This
area may be selected by CP/M's "USER n" command, "n"
being the number of the area (0 ... 15). The "USER"
commands allow only access to the files in the
selected area and to the files in the 0 area which
are designated as "system" files.
- 4 -
4. File Management by the MS-DOS Emulator
The emulator is almost transparent with regard to MS-DOS
disk and totally transparent when you deal with CP/M disks.
The only differences concern the handling of directory files,
time stamping and the use of passwords on MS-DOS disk. The
directory files are gathered into the "USER 1" area. They can
be listed with:
USER 1
DIR
Only the files described in the currently selected
directory file can be handled with CP/M commmands or BDOS
functions. The directory files are selected with the CD
command.
The DEMO version of the emulator does not time stamp MS-
DOS disks.
Passwords cannot be used on MS-DOS disks, because MS-DOS
doesn't allow it.
A special entry, named "other.dir", is present in the
"USER 1" area. There is no file with this name on the disk.
The entry is created by the emulator in order to allocate the
sectors belonging to files with no entries in the current
directory. In this way the files are protected against
overwriting.
5. Commands
The MS-DOS emulator is started by:
MSDOS
After the program is started, the following message is
displayed:
MS-DOS Emulator V1.03 # DEMO
(c) SanDES 1990
A third line follows, displaying supplementary information
(the computer type f. ex.). If the MS-DOS Emulator is already
started, the following warning is displayed:
*** MS-DOS emulator already started ***
- 5 -
Another message may be displayed:
*** Not enough common memory ***
This means that there is not enough room for the emulator's
buffers in RAM (it needs at least 2 Kbytes), because there are
other programs in the upper area of RAM (SUBMIT, GET or PUT f.
ex.). This problem may be solved by starting the MS-DOS
Emulator before the other programs.
The emulator can be stopped by:
MSDOS OFF
The emulator has a built-in command for selecting
directory files. It can be used as follows:
CD directory file
"directory file" becomes the current directory.
CD ..
The directory containing the entry describing the currently
selected directory file becomes the new current directory.
CD
Resets the drive and selects the "\" directory as current
directory. This command can be used after a disk change,
instead of CTRL/C.
CD .
Resets the drive and retains the same cur