MOS 6502

The MOS Technology 6502, often referred to as simply 6502, was a low-cost 8-bit processor that was produced by MOS Technology, and later Commodore International. It became widely used in early computers, such as the Apple I, Commodore PET and VIC-20, as well as early game systems, such as the Atari 5200.

History
Electrical engineer Chuck Peddle had worked on the Motorola 6800 processor in 1973, which was priced at US$300 per unit in a kit. Motorola turned down his proposal to produce a simplified processor to meet marketplace demand for a lower-cost processor. Peddle and some other Motorola engineers then left for MOS Technology, where they formed a small team to design the 6502, which became available in 1975 at a fraction of the cost of the Motorola 6800 and Intel 8080.

In November 1975, Motorola filed a lawsuit against MOS Technology for patent infringement and misappropriation of trade secrets. MOS settled the case in March 1976 for $200,000 and cancelling the 6501 processor, which was socket-compatible with the 6800. In November 1976, MOS was acquired by Commodore International, which produced the 6502 and variants for its own computer line.

Steve Wozniak obtained early units of the 6502 from Chuck Peddle for use in the Apple I computer. After Commodore acquired MOS, Apple obtained subsequent processors from Synertek for their Apple II and III series.

Variants
The 6502 design was revised many times and licensed to different manufacturers:
 * MOS MCS6502 - a rare early version of the MOS 6502 which was used in the Apple I computer.
 * Synertek SY6502 - a second-sourced version used in Apple II computers after MOS was acquired by Commodore.
 * Synertek SY6502A/B - a faster version used in Apple III computers.
 * MOS 6502B/C - even faster versions used in the Atari 400, 800, 5200, and 7800.
 * NCR/GTE 65C02 - a low-power CMOS version used in the Apple IIc and Apple IIe Enhanced.
 * MOS 6507 - an ultra low-cost version used in the Atari 2600.
 * MOS 6510 - an enhanced version used in the Commodore 64.
 * WDC 65C816 - a backwards-compatible 16-bit version used in the Apple II GS.