MOS Technology
MOS Technologies was a microprocessor design company started by ex-Motorola designers led by Chuck Peddle, who left the company shortly after the release of the Motorola 6800.
Their first project was the 6501, a low-cost (smaller chip) version of the 6800, realized by simplifying the decoder stage. There were no op-codes with the value xxxxxx11, reducing the 1-of-4 decoder to a single NAND gate. Instructions with the value xxxxxx11 actually executed two instructions in parallel, some of them useful. The 6501 was pin-compatible with the 6800, yet cost less than 1/4 as much, and ran faster.
Motorola launched a lawsuit almost instantly, and eventually MOS Technologies agreed to not sell the 6501. Instead they turned to the 6502, a very similar chip that was no longer pin-compatible. This seemed to satisfy Motorola (although it likely wouldn't today) and the 1MHz 6502 became available in September 1975 for a mere $25. Due to it's speed it outran the more complex and expensive Intel 8080 and Zilog Z80 series, but cost less and was easier to work with than either. The 6502 would go on to be one of the most popular chips of it's day.
A number of different versions of the basic 6502, the 6503 through 6507, were offered in 28-pin packages for lower cost. The various models removed signal or address pins, but of these it appears only the 6507 saw widespread use. They also released a series of similar CPU's using external clocks, which added a "1" to the name in the 3rd digit, the 6512 through 6515. These were useful in systems where the clock support was already being provided on the motherboard by some other chip. The final addition was the "crossover" 6510 with additional I/O ports.
MOS had also designed a simple computer kit called the KIM-1, primarily to "show off" the 6502 chip. Shortly after completing it, MOS was purchased by Commodore to ensure supplies of chips for their calculator line. At Commodore Peddle convinced the owner, Jack Tramiel, that calculators were a dead-end, and that home computers would soon be huge. This led to the Commodore PET computer. The PET was developed by MOS, but was manufactured and marketed by Commodore.
A number of companies licenced the 650x line from MOS, including Rockwell International. In 1978 they set up the Western Design Center (WDC) under the direction of William Mensch in Mesa, AZ from Norristown, PA. By this point many of the original team had left Commodore (including Mensch), one result being that the newly-completed 6522 (VIA) chip was left undocumented for years.
Western Design Center continued work on CPU designs. Their first major upgrade to the line was the 65816, a fairly simple 16-bit upgrade of the original 6502 that could also run in a 8-bit mode for compatibility. A planned 32-bit 65832 CPU was never released.
Today the company licenses a subset of their original catalog for production by 3rd parties. They have moved the entire line to CMOS and the CPU's are now known as the 65C02 and 65C816. Microcontroller versions of both with an embedded UART and several timers are known as the 65C134 and 65C265 respectively. The VIA also soldiers on as the 65C22.
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This article (or an earlier version of it) contains material from FOLDOC, used with permission.