expansion cards.

The first 400,000 16 KB mainboards ("16KB-64KB" ID) sold until March 1983 can be upgraded to a maximum of 64 KB onboard without using slots, and the later 64 KB revision ("64KB-256KB" ID) to a maximum of 256 KB on the motherboard. RAM cards can upgrade either variant further, for a total of 640 KB conventional memory, and possibly several megabytes of expanded memory beyond that,