Apple 1977

Shortly after the 8080, Motorola introduced the 6800. Some designers then started MOS Technologies, which introduced the 650x series, based on 6800 design (not a clone for legal reasons), and including the 6502 used in Commodores, Apples and Ataris. Steve Wozniak described it as the first chip you could get for less than a hundred dollars (actually a quarter of the 6800 price). Unlike the 8080 and its kind, the 6502 had very few registers. It was an 8 bit processor, with 16 bit address bus. Inside was one 8 bit data register, and two 8 bit index registers and an 8 bit stack pointer (stack was preset from address 256 to 511). It used these index and stack registers effectively, with more addressing modes, including a fast zero-page mode that accessed memory addresses from address 0 to 255 with an 8-bit address that speeded operations (it didn't have to fetch a second byte for the address). The 650x also had undocumented instructions. As a side point, Apples, which were among the first microcomputers introduced, are still made, now using the 65816, which is compatible with the 6502, but has been expanded to 16 bits (including index and stack registers, and a 16-bit direct page register), and a 24-bit address bus. The Apple II line, which actually includes the Apple I, is the longest existing line of microcomputers. Back when the 6502 was introduced, RAM was actually faster than CPUs, so it made sense to optimize for RAM access rather than increase the number of registers on a chip.

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