MOS Technology 6502 - Acceleration

Acceleration

Many users of 1 MHz 6502-based systems soon wished their computers could go faster. As the 6502 is externally-clocked, upgrading the speed involved more than dropping a faster chip into the processor socket; many other components would also need to be modified. To meet user demand, a number of companies sold hardware to speed up those systems. These "accelerators" included a modicum of high-speed RAM and glue circuitry used to synchronize the faster processor with the computer's original RAM and its peripherals. For example, the Apple II floppy disk relied on software accessing the controller's I/O registers with critical timing; Apple II accelerators were therefore designed to fall back to 1 MHz during disk access. The first accelerators were circuit boards; some later accelerators (such as the Zip Chip) miniaturized the processor and support circuits to fit into a DIP package that was plug compatible with the original processor.