CP/M cartridge retail box
Back in 1983 there was this great idea of expanding the Commodore 64 with the then popular (but declining) base of serious business software from the CP/M side of the world by creating a cartridge with a z80 processor inside, and a special port of the CP/M operating system that would take over the C64 letting you run real programs like Fortran, Cobol and the far better (and updated) Microsoft Basic v5!
However as always the major failing of CP/M was the massively different and incompatible diskettes of every platform. The Commodore 64, lacking in RS-232 ports, and it’s incredibly incompatible 1541 drive rendered it nearly impossible for the average home user to transfer any programs in the specially formatted CP/M diskettes for the cartridge. Not being able to read a standard 1541 diskette would prove to be it’s undoing.
While messing around in Vice, I saw that this cartridge is emulated now! A quick search led me to zimmers.net where I was able to then locate the needed cpm.d64.gz, and I was booted up into CP/M and of course that hit the first snag which is of course, where is the software?
Well another search brought me to the package ‘ctools‘ which I quickly built on the Linux subsystem for Windows (I had to add -fpermissive to get it compile..), and now I could take that CP/M diskette delete the contents, and for the heck of it insert in Zork.. Of course where to find Zork along with other CP/M software? The zip zork123_80.zip can be located on retroarchive.org, even fun things like Microsoft BASIC v5.21 (Interpreter), along with the manual.
CP/M only recognized a single drive, so you have to swap diskettes (Such a typical Commodore 64 experience), and here we go!
Naturally the Commodore 64’s 40 column mode is… terrible.
However even back in 1984, a fine program aptly called soft80.com sets up the Commodore 64 in high resolution graphics mode, and emulates an 80 column mode. Even better, the magic for the most part happens on the 6502 side, meaning it doesn’t take away from the precious memory on the CP/M side.
Zork 1 under CP/M / Soft80
Its worth noting that although Infocom games are dreadfully slow on the Commodore 64, playing under CP/M is also dreadfully slow, taking some 10-15 seconds to complete a command.
At least under emulation there is the warp mode. And what took an hour to put together would have been months no doubt in the 1980’s ending in the CP/M cartridge going into a drawer to never be seen again.
A Z80 on a cart is pretty interesting. It would have been interesting if other CPUs had made their way, a 68000 would have been interesting to have bridge the 8 bit world out, or even if Commodore had tried to put an 8088 onto that card, as early PC’s were nowhere near the 640kb hard disk wielding monsters they would become much later. Naturally one could only dream of the power of an 80386 or the once vaunted NS32016