The MOS Technology 6502 is an 8-bit microprocessor introduced in 1975 by MOS Technology of Norristown, Pennsylvania. Designed by a team led by Chuck Peddle that had left Motorola, it was conceived to be dramatically cheaper than competing parts such as the Motorola 6800 and the Intel 8080, and it launched at a price low enough to make the microprocessor itself affordable to hobbyists and small manufacturers for the first time. That low cost, more than any single architectural feature, is why the 6502 became one of the defining chips of the personal-computer era.
The MOS MCS6500 family preliminary datasheet describes the part as an 8-bit parallel processor with a 16-bit address bus, giving direct access to 65,536 bytes of memory. The datasheet documents the register set and the family’s range of pin-compatible and bus-compatible variants, including the 6502 itself and reduced-pin members such as the 6503 through 6507. The design emphasized efficiency: a wide set of addressing modes, a fast zero-page region of memory that could be used almost like an extended register file, and a pipelined fetch that let many instructions overlap execution with the next fetch.
The 6502 was deliberately frugal in transistor count, which kept manufacturing yields high and prices low. It used a simple, regular instruction set well suited to hand-written assembly language, and its zero-page and indexed addressing modes let tightly written code run quickly despite the chip’s modest clock speed. These traits made it a favorite of assembly programmers who squeezed games and graphics routines into very small amounts of memory.
The chip’s commercial reach was enormous. The 6502 and its close relatives powered the Apple II, the Commodore PET, VIC-20, and Commodore 64, the Atari 400/800 and 2600, the BBC Micro, and, in a customized form, the Nintendo Entertainment System. Because the same processor family appeared across so many machines, programming knowledge and techniques transferred readily from one platform to another, helping to seed a broad community of microcomputer programmers.
The 6502’s influence outlived the 8-bit era. The closely related design lineage continued through Western Design Center’s 65C02 and 65C816, the latter powering the Apple IIGS and the Super Nintendo. Decades later the simple, well-documented 6502 remains a standard teaching example for computer architecture and assembly language, a direct legacy of the cheap, capable chip that helped put computers in millions of homes.