Madison Computer Z-RAM

  • The Z-RAM from Madison Computer is an expansion board for Commodore PET/CBM computers. It was known in Europe as the CP/Maker. Z-RAM adds 64K of RAM and a Z80 coprocessor to allow the PET to run the CP/M operating system.

    Z-RAM functions as a configurable 64K RAM expander for the PET, similar to the 8096 board, but not compatible with it. To run CP/M, the PET loads CP/M into the expansion RAM and then switches on the Z80. The expansion RAM is then only accessible to the Z80. The board adds a 6520 PIA to the PET memory map and a special terminal program communicates with the Z80 side through I/O lines.

    More photos of the Z-RAM can be found in this Flickr album.


    User’s Manual

    The manual includes the schematic and block diagram:
    Block Diagram


    The software came on one double-sided disk that the manual refers to as the “Master Disk”. The front side is 8050 format and the back side is 4040 format:

    Master Disk (D64: 4040 Format)
    Master Disk (D80: 8050 Format)

    Each side of the Master Disk includes programs for the PET side and a CP/M filesystem image contained in a relative file called CP/M DRIVE A. The PET programs appear to be the same on each side but the 8050 side has a larger CP/M DRIVE A file and an additional one named CP/M DRIVE B.


    The Z-RAM was developed in the USA by Madison Computer, who sold it directly. In Europe, the Z-RAM was known as the “CP/Maker”. It was sold through Tamsys Ltd. (UK), Data Becker (Germany), and Vector International (Belgium).

    CP/Maker Listing (Using Your Computer: Commodore Applications Catalogue)
    CP/Maker Advertisement (German “Chip” magazine)


    Review (Commodore Magazine, Apr/May 1982)
    Review (Interface Age, June 1982)
    Review (Microcomputing, Oct 1983)
    Advertisement (Commodore Magazine, Aug/Sep 1982)
    Advertisement (Commander, Aug 1983)


    This page was made possible by the following people:

    • Ruud Baltissen of the Netherlands – Ruud found the Z-RAM board and gave it to me. It was unidentified at the time and sparked a long thread on cbm-hackers as we tried to figure out what it was and how it worked.
    • Ed Johnson of St. Augustine, Florida, USA – Ed found an 8032 with a Z-RAM board installed and a binder with the manual. He sent me photocopies of the manual.

    Thank you for all of your help!