TRS80s and TRSDOS (Was: Microsoft open sources GWBASIC

Fred Cisin cisin at
Thu May 28 20:16:03 CDT 2020

> > It had a memory map that was incompatible with CP/M.  BASIC in ROM at 
> > the bottom, and RAM at the top.
> > FMG marketed a "relocated" CP/M for it, but that never caught on. 
> > numerous incompatabilities, and few commercial programs were happy 
> > with the TPA having been moved.
> > Howard Fulmer ("Parasitic Engineering") sold [expensive] daughter 
> > boards for the Model 1 to remap the memory, and convert the FDC for 8" 
> > SSSD.
> > Also Omikron. Both were walking distance from me in Berkeley, but they 
> > were much too expensive to catch on.  (I eventually found used ones)
> > Similar products became available after the model 3 came out, and 
> > Radio
> > Shack included CP/M capability in the Model 4 (and 80 column screen)

>> TRS80 base model had 4K of RAM (upgradable to 16K), and "Level 1 BASIC" in 
>> ROM at the bottom (preventing easy use of CP/M),

On Thu, 28 May 2020, Bill Gunshannon via cctalk wrote:
> KiloBaud Microcomputing  April 1979
> Page 148: FMG Corporation -- CP/M for the TRS-80
> That wasn't the one I used but the magazine was sitting right here
> and I don't have time to dig up which one I had.
> CP/M was available for all the TRS-80's never looked to see how it
> got around the ROM stuff, but I know it did.

FMG sold a MODIFIED/RELOCATED CP/M.  It put the TPA (Transient Program 
Area) in a different place, and meant that TPA was limited to about 32K

Parasitic Engineering's "Shuffleboard", and Omikron "Mapper" (and Memory 
Merchant?) placed daughterboards under the Z80 to rearrange the memory 

FMG's relocation of the OS and TPA meant that a LOT of commercial CP/M 
software woudn't run on it.  But some would!

Nevertheless, when I was teaching a TRS80 based operating systems class, I 
used FMG on my demo machine (plywood mounted, that I carried in to UC 
Berkeley Evans 10, and used the BIG overhead monitors) to be able to show 
the class everything that I wanted to show them about CP/M.  Even stuff 
like use of DDT and also creating a zero byte executable file for 
restarting a program.
I don't remember whether FMG was CP/M 1.4 or 2.x (I think that it was 
2.2), but it was "real" CP/M, enough to use as a teaching/demo tool, but 
with TPA too constrained to run Wordstar with large files, or to run 
IOW, not suitable for some of the work that I would use CP/M for.
When my business included resale of commercial software, I bought ten 
copies.  I only sold about half of them.

> Even had CP/M 3.0
> for the Model4 and the Model 2/12/16.

Yes, indeed!  Radio Shack marketed the CP/M 3.0 as "CP/M PLUS".

More information about the cctech mailing list