What major late '70s and early '80s 8-bit microcomputers did not offer a CP/M option?

Through the early '80s CP/M was one of the more popular systems, especially for business applications. One advantage it had was that it was expected to run on all manner of systems, so software generally had the ability to be configured for various terminals and other hardware.

For systems already based on the Z80, such as the TRS-80 Model I/III/IV and the ZX Spectrum, this sometimes required a hardware modification to tweak the address decoding; you could do this yourself or third-party vendors often offered the modification. It wasn’t unusual for later models in the series (TRS-80 Model 4, Spectrum 3+) to be changed to directly offer CP/M support.

For systems with MOS or Motorola CPUs it was usually even easier (if more expensive): just pop in a card or cartridge with a Z80 processor. Examples include:

The PET seems to be the one major exception to this. Were there others? (If you’re not sure about the system you’re thinking of, Wikipedia has a List of computers running CP/M.)

Since CP/M required disk drives, I think it’s fair to limit answers to systems where the majority of the installed base had a drive, or they were at least very commonly used. (So no ZX81, sorry fans.)


I think it’s simpler to find the non-Z-80 machines that had CP/M rather than list off the ones that didn’t. For instance I’m pretty sure that the TRS-80 Color Computer didn’t have an option for CP/M.

Nice! I’m pleasantly surprised to see the Spectrum. Amstrad’s CPC, too, can run CP/M.

As for those which can’t, the tripwire here is ‘major’ - there are so very many micros from that time! I propose we don’t try to pick apart that distinction.

Just a nitpick: the BBC Micro has a “Tube second processor interface” - not a slot.

The later BBC Master had the same interface, which takes a (very short) umbilical to a box placed to the side of the machine. It also had a pair of headers internally, used for an internal second processor: same logical and electrical interface but different form factor. There was also an option for an empty external box which accepted the internal type of second processor, at extra cost.

I suppose that if we get into the nitty details, technically, you’re correct that there wasn’t an option for CP/M, because there were at least three. :-)

Well, given the way the numbers are going so far (6 with, one without), that doesn’t seem the case.

Oh, wait; I lied about those numbers. Make it 7-0:

I’m probably in the extreme minority here in that I hadn’t heard of CP/M at the time. I mean, I saw print ads for Heathkit, but I didn’t know anything about S100 or CP/M or anything like that.

So for me, home computers were defined by what I could try out in retail store displays - no mass storage, just whatever you got when you turned it on. That meant the default interactive BASIC interface.

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Don’t forget that CP/M isn’t just about the Z80, but originally about the Intel 8080/8085 (to which the Z80 is compatible). Provided there’s a disk drive available, these machines should be capable of running CP/M as well.

Early in the PC’s life a popular upgrade was replacing the 8088 with the pin compatible NEC V20 processor. That ran 8088 code slightly faster but also had a Z80 mode that allowed the PC to be used as a CP/M machine (CP/M-86 was one of the OSes available for the PC, but it had far less software for it than the 8 bit version). The most popular CP/M software had already been ported to the PC and DOS at launch or soon after, but some people still felt there were many interesting 8 bit programs missing. That phase probably lasted less than 6 months in 1982/1983.

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I can well imagine for business continuity a company might buy a CP/M system to run the software they know in the way they know, rather than hopping to DOS on the PC.

BTW, Amstrad’s PCW was made up until 1998. I wonder (idly) what other CP/M systems you could still buy as late as that.

And here’s a machine I didn’t expect to have a Z80 add-in for CP/M:

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Also, don’t forget, that the different CP/M system integrated in different ways.

The Apple CP/M leveraged the Apples hardware quite well: display, keyboard, floppies. It was a Z80 with dedicated RAM.

The Atari one, however, was basically a full boat computer that the Atari connected to as little more than a dumb terminal.

So, some of these integrations were more substantial than others.

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