MOS Technology 6502

The MOS Technology 6502 (typically pronounced "sixty-five-oh-two" or "six-five-oh-two") is an 8-bit microprocessor that was designed by a small team led by Chuck Peddle for MOS Technology and was launched in September 1975. The design team had formerly worked at Motorola on the Motorola 6800 project; the 6502 is essentially a simplified, less expensive and faster version of that design using depletion-load NMOS technology that made using the microchip in computers much cheaper.

When it was introduced, the 6502 was the least expensive microprocessor on the market by a considerable margin. It initially sold for less than one-sixth the cost of competing designs from larger companies, such as the 6800 or Intel 8080. Its introduction caused rapid decreases in pricing across the entire processor market. Along with the Zilog Z80, it sparked a series of projects that resulted in the home computer revolution of the early 1980s.

Home video game consoles and home computers of the 1970s through the early 1990s, such as the Atari 2600, Atari 8-bit computers, Apple II, Nintendo Entertainment System, Commodore 64, Atari Lynx, BBC Micro and others, use the 6502 or variations of the basic design. Soon after the 6502's introduction, MOS Technology was purchased outright by Commodore International, who continued to sell the microprocessor and licenses to other manufacturers. In the early days of the 6502, it was second-sourced by Rockwell and Synertek, and later licensed to other companies.

In 1981, the Western Design Center started development of a CMOS version, the 65C02. This continues to be widely used in embedded systems, with estimated production volumes in the hundreds of millions.

The origins of the 6502 chip date back to 1960, after the Soviet Union launched the first artificial Earth satellite – the Sputnik 1. During this time, Chuck Peddle worked at General Electric as an engineer-in-training, designing tests and systems for missiles and spaceships. As he advanced into his engineering career, he found room-sized computers to be a flawed model of centralized intelligence, and instead, considered distributing it locally. However, General Electric sold its computer division to Honeywell in 1970, liquidating the entire section he worked in.

Undeterred, Peddle took this severance and started his own company in 1972 to make intelligent terminals for word-processing. Shortly after, Peddle found himself in a technological struggle; even though electronics were evolving at the time, it was still ridiculously complex to run the system he conceived. His idea required a microprocessor that would be capable of running programs. However, many companies were competing on the same technology for the same reason, including Motorola.

Motorola started the 6800 microprocessor project in 1971 with Tom Bennett as the main architect. Motorola's engineers could run analog and digital simulations on an IBM 370-165 mainframe computer. The chip layout began in late 1972, the first 6800 chips were fabricated in February 1974 and the full family was officially released in November 1974.

John Buchanan was the designer of the 6800 chip and Rod Orgill, who later did the 6501, assisted Buchanan with circuit analyses and chip layout. Bill Mensch joined Motorola in June 1971 after graduating from the University of Arizona (at age 26). His first assignment was helping define the peripheral ICs for the 6800 family and later he was the principal designer of the 6820 Peripheral Interface Adapter (PIA). Bennett hired Chuck Peddle in 1973 to do architectural support work on the 6800 family products already in progress. He contributed in many areas, including the design of the 6850 ACIA (serial interface).