What is it?

This is a cartridge that adds 24KB RAM to bank 15 in the user expansion space of the memory map (address 0x2000 thru 0x7fff). It uses 3 static RAM (SRAM) devices along with decoupling capacitors in its design (brand of SRAM chip and capacitor may vary from photos - whatever I have in parts stock at the time). Each newly built RAM cartridge is burn-in tested using memtest by Nick Hampshire for 30 minutes prior to shipment. This RAM expansion cartridge is for the Commodore B Series computer models (sometimes known as CBM-II models) such as the USA/Canada B500, B128-80, CBM 128-80, and CBM 256-80 and in the EU 610, 620, 710, and 720 and has been tested for compatibility in these models. It should also work in the P500 models and protoype models such as the B700 but has not been tested with those models.

Why did you make it?

I had a commercial cartridge from 1983 that provided similar capability, but when that became unrepairable I designed my own replacement for its purpose. You can occassionally find it useful to have this extra RAM in bank 15 when tinkering on a program, or trying to develop something you might want to put into a cartridge ROM later. General retrocomputing stuff.

What makes it special?

Anything for the Commodore B Series computers is ultra rare as commercially the line was abandoned by Commodore as the IBM PC established dominance in the business world. I think the Commodore B Series computers are important in the history of Commodore Business Machines, and so I was motivated to do this design for the fellow collectors of them.