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MOS Technology, Inc. ("MOS" being short for Metal Oxide Semiconductor), also known as CSG (Commodore Semiconductor Group), was a semiconductor design and fabrication company based in Norristown, Pennsylvania, in the United States. It is most famous for its 6502 microprocessor and various designs for Commodore International's range of home computers.
A 1973 MOS Technology advertisement highlighting their custom integrated circuit capabilities.
MOS Technology, Inc. was originally started in 1969 by Allen-Bradley to provide a second source for electronic calculators and their chips designed by Texas Instruments (TI). In the early 1970s TI decided to release their own line of calculators, instead of selling just the chips inside them, and introduced them at a price that was lower than the price of the chipset alone. Many early chip companies were wiped out in the aftermath; those that survived did so by finding other chips to produce. MOS became a supplier to Atari, producing a custom single-chip Pong system.
Things changed dramatically in 1975. Several of the designers of the Motorola 6800 left Motorola shortly after its release, after management told them to stop working on a low-cost version of the design. At the time there was no such thing as a "design-only" firm (known as a fabless semiconductor company today), so they had to join a chip-building company to produce their new CPU. MOS was a small firm with good credentials in the right area, the east coast of the USA. The team of four design engineers was headed by Chuck Peddle and included Bill Mensch. At MOS they set about building a new CPU that would outperform the 6800 while being similar to it in purpose. The resulting 6501 design was somewhat similar to the 6800, but by using several simplifications in the design, the 6501 would be up to 4 times faster.