Well, ram upgrades on those machines didn't just plug into slots. Various C64 upgrades were replacement RAM chips, or piggy backed on the existing chips. Same f

Well, ram upgrades on those machines didn't just plug into slots. Various C64 upgrades were replacement RAM chips, or piggy backed on the existing chips. Same for the II line, although frequently there were RAM upgrade slots (like the IIGS for example). But beyond that most of these machines had the ram and slots in the same clock domain (aka a "local bus"). So a plugin card's ram basically ran at the same rate as the onboard ram. Of course there were often banking issues on the 8bit machines, but that happened regardless of where the ram was located as things like the 128k IIC (a machine without slots) were banked from the factory, and various mod level upgrades replaced various chips on the board, until the later revisions when apple provided a sanctions mechanism for upgrading the machine to 1M.