Task: Run the CP/M Operating System on Your Atari 8-Bit Computer using an Upgraded Indus GT Floppy Drive
Needed: Web Browser, Floppy Disks, ProSystem Software or Similar, DT-80 Cartridge or Similar
Time: 30-60 mins
I have a fascination with the CP/M operating system because I never used it back in the day. CP/M was one of the early operating systems available for computers with 8080 and Z-80 processors. It was developed by Gary Kildall and first released in 1974. It came close to becoming the dominant operating system, but was overtaken by DOS. It was common for 6502-based computers like the Apple II and the Atari to come up with ways to run CP/M to give users access to all the software written for CP/M on Z-80 computers like the Sinclair ZX Spectrum. Here is a list of computers which could run CP/M.
There were several CP/M options for the Atari 8-bit computers including the ATR8000 which was a headless Z-80 computer that would use the Atari and its monitor as a dumb terminal. Interestingly, the popular Indus GT disk drive for the Atari line was build using a Z-80 processor. They wisely included a set of expansion pins for adding RAM to make it a real computer capable of running CP/M and compatible software. A modern RAM upgrade for the Indus GT is the SRAM Charger developed by Jürgen van Radecke and currently sold in the U.S. by Gavin Haubelt from the Vintage Computer Center. I have previously posted about how to do this simple and quick upgrade. This is required for this project. The instructions below show step by step how to get an upgraded Indus GT to boot CP/M.
Before you begin, make sure your Indus GT has 64K of RAM from an upgrade such as the SRAM Charger.
The instructions and ATR files used here were taken from an Atari Age post on October 6, 2018 by Atari Age user TF_HH (i.e. Jürgen van Radecke) and worked well for me. I made a few minor edits for clarity. Note that these instructions are based on the posts on the ‘trub Atari website‘ where there is more detailed information. Note that the trub site refers to retrobits.net for files which does not seem to be live.
1. Use a sector copier to copy the following files each to one real floppy disk using your Indus GT drive. I used the AtariMax ProSystem system software to copy each ATR file to a floppy over SIO2PC. Here is a .zip file with all four ATRs.
Indus RAM Charger Check.atr
Indus RAM Charger 40-80 Terminal.atr
Indus RAM Charger CPM Boot.atr
Indus RAM Charger CPM BIOS.atr
2. Boot the “Indus RAM Charger Check” disc with no BASIC (OPTION held) from your Indus GT drive. Press “L” on the DOS menu and RETURN, enter “CPMTOOL.COM” and RETURN.
3. Press “1” to test your SRAM charger. First the installed ROM version will be displayed. If your version is below 1.20, then CP/M is not possible! See the original post for instructions on how to proceed. Briefly, you will need to flash a new ROM chip for the Indus GT.
4. Test your SRAM charger by pressing “2”.
5. Insert the “Indus RAM Charger CPM Boot” disc and press “2” (Fix CP/M boot). Confirm with “Y”. A few sectors will be written. This step and the next one fix some sectors needed to get this to work.
6. Insert the “Indus RAM Charger CPM BIOS” disc and press “2” (Fix CP/M boot). Confirm with “Y”. A few sectors will be written.
7. Switch off computer, insert the “Indus RAM Charger 40-80 Terminal” disc and power on with OPTION held. Note that I also inserted the DT-80 cartridge to take advantage of 80 columns of text which is optimal for CP/M. There are other 80-columns options for the Atari.
8. DOS XL will be booted and some hints how to continue. Press “F” for the 40 column terminal or “E” for the 80 column version, then RETURN
9. After the terminal software is loaded, only a light green cursor in the upper left corner will be visible. That´s normal.
10. Insert the “Indus RAM Charger CPM Boot” disc in your Indus GT drive.
11. Press the “DRIVE TYPE” button on the front of your drive, hold it down and then press the ERROR key.
12. A beep will be audible. The drive should now boot CP/M. The message “FUTURE CPM 2.2 REV 1.0 – Hit RETURN to continue” appears.
13. Hit RETURN and a prompt “A>” with a Digital Research copyright notice will be displayed.
That´s all. Now you can load CP/M programs and use the commands found in the disc(s). Enter “DIR” <RETURN> to see the available CP/M commands.
Thanks to Jürgen van Radecke for developing the SRAM Charger card for the Indus GT and for providing clear instructions on how to boot CP/M.
There are instructions at the end of this post on the trub website for how to load and run CP/M software.
A modern solution to running CP/M on the Atari is by using the FujiNet device with the Run CPM emulator.