B1024 RAM Expansion Board

  • The B1024 is a plug-in RAM upgrade for CBM-II computers that was designed and sold in the mid-1980’s by Gary Anderson under the name Anderson Communications Engineering. Gary was a member of the Chicago B128 Users Group (CBUG). The B1024 mounts on the internal expansion headers and provides a full 1 megabyte of RAM using 41256 DRAMs. The original 4164 DRAMs on the CBM-II mainboard are no longer needed and can be removed when the B1024 is installed. The B1024 also has a 6264 SRAM that adds an additional 8K of RAM to the system bank.

    Bill Degnan found a bare board and traded it to me in 2013. I made contact with Gary Anderson but unfortunately he no longer had the schematic. Using photos of an assembled board as a guide, I acquired the necessary parts and finished the board in that same year. The photo above shows my completed board. It works and has been installed in my B128 ever since.

    The power-on RAM test takes a very long time to complete with RAM in all the extra banks. I have modified the KERNAL to only test one byte of each page so that the RAM test completes almost instantly. The B1024 has headers to allow another board to be stacked on top. Articles in the CBUG Escape newsletter indicate that the 8088 coprocessor board can be used with it. I haven’t tried this yet.

    Bare Board Photos

    Since no schematic for the board has been found, it will need to be reverse engineered. I took photos of the bare board before assembling it to help with this. I may do it eventually but I am providing the photos here in case someone else wants to tackle it.

    B1024 Bare Board (Top Side)
    B1024 Bare Board (Bottom Side)
    B1024 Components


    B1024 Photo Set on Flickr