C64 CP/M Cartridge

The cartridge that makes a C64 a “dual processor” computer: Commodore’s CP/M cartridge for C64 contains a Z80 CPU and comes with version 2.2 of the CP/M operating system. Here are some pictures.

The CP/M operating system was popular for its large library of business applications. It required an Intel 8080 compatible CPU, so it didn’t work on the C64. Commodore’s CP/M cartridge from 1983 does nothing more than add a Z80 (which is 8080 compatible) to the C64. The OS and its applications ran on the Z80 CPU, which could switch back to the 6502 for screen, keyboard and disk access.

The device was unsuccessful on the market because the Commodore 1541 disk drive was unable to read any of the variants of the MFM disk format that most software was released in, and software manufacturers were reluctant to release 1541 disks – so there was simply no software. Commodore learnt from their mistake: The C128 (1985) came with the additional Z80 CPU on the mainboard and CP/M 3.0, and the 1571 disk drive had the ability to work with MFM disks.

This is the box. The back says:

The Commodore 64 CP/M® 2.2 Operating System

Now you can turn your Commodore 64 into a DUAL PROCESSOR home computer. The Commodore 64 CP/M® version 2.2 Operating System lets you expand the software applications you can use with your Commodore 64. When you add this easy-to-install system, you can begin using some of the many available CP/M® programs, including these:

  • Widely used business applications
  • Word processing
  • High level computer language compilers (e.g., COBOL, FORTRAN]
  • And many other specialized software programs

The easy-to-install Commodore 64 CP/M® Operating System includes all these items:

  • A Z80 microprocessor, called the Commodore 64 CP/M Cartridge
  • The CP/M® disk, which contains both the CP/M® operating system and some utility programs
  • A user manual, which contains instructions for using the CP/M® Operating System and utilities

*CP/M is a registered trademark of Digital Research Incorporated


© Copyright 1983 by Commodore Electronics, Ltd. All rights reserved. No part of the programs or manual included in this work may be duplicated, copied, transmitted or reproduced in any form or by any means without the prior written permission of Commodore.

Commodore Business Machines, Inc. • 1200 Wilson Drive • West Chester, PA 19380

The cartridge only says “Commodore 64 CP/M® Cartridge / CP/M is a trademark of Digital Research”. There are no other labels.

The board (ASSY. NO 326232 REV. B; FAB NO 326229 REV. B) contains the 3 MHz Z80 CPU as the only major chip.

The users manual is available from archive.org. The operating system comes on a 1541-formatted disk (cpm22.d64).

0 "CP/M DISK       " 65 2A  
1     "CPM"               PRG  

From the Commodore DOS point of view, it only contains a small boot program. The rest of the disk uses the CP/M filesystem:

A: MOVCPM   COM : PIP      COM  
A: ED       COM : ASM      COM  
A: DDT      COM : LOAD     COM  
A: DUMP     COM : DUMP     ASM  
A: COPY     COM : CONFIG   COM          


2 thoughts on “C64 CP/M Cartridge”

  1. I had that one, and even wrote a disk driver for it, using my (somewhat) faster floppy transmission protocol so it loaded things faster from disk (1541). I could not sell it though, because there seemed to be no one else who used that, at least not in Germany.

    That CP/M system was not bad IMO, but I was young and had no clue.

  2. Problem 1: The Z80 couldn’t run in parallel to the 6510 (same as in C128).
    Problem 2: C64 with this cart was a rather slow CP/M system, also in terms of CPU poer (same as C128)
    Problem 3: Only 40 characters in a row, not really suitable for CP/M (on the C128 they put additional video chip to Z80, with a separate video output, but it’s software driver was very slow)
    Problem 4: When the cart was released, CP/M popularity was rapidly declining (when C128 was released – CP/M was considered seriously outdated)
    Problem 5: Transient Program Memory area was rather low while using this cart
    Problem 6: This cart works only on early C64 models, which has a buggy video chip; it doesn’t work with fixed VIC II.

    Seriously… CP/M on both C64 and C128 is a pure disaster. GEOS forever!

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