Source : Free On-Line Dictionary of Computing

MOS Technologies
     
         A {microprocessor} design company started by some
        ex-{Motorola} designers, shortly after the {Intel 8080} and
        {Motorola 6800} appeared, in about 1975.  MOS Technologies
        introduced the {650x} series, based on the {Motorola 6800}
        design, though they were not exact clones for legal reasons.
     
        The design goal was a low-cost (smaler chip) design, realized
        by simplifying the decoder stage.  There were no instructions
        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 paralell, some of them
        useful.
     
        The 6501 was pin-compatible with the 6800 for easier market
        penetration.  The 650x-series had an on-chip clock oscillator
        while the 651x-series had none.
     
        The 6510 was used in the {Commodore 64}, released September
        1981 and MOS made almost all the ICs for Commodore's {pocket
        calculators}.
     
        The {PET} was an idea of the of the 6500 developers.  It was
        completly developed by MOS, but was manufactured and marketed
        by Commodore.  By the time the it was ready for production
        (and Commodore had cancelled all orders) MOS had been taken
        over by {Rockwell} (Commodore's parent company).  Just at this
        time the 6522 (VIA) was finished, but the data sheet for it
        was not and its developers had left MOS.  For years, Rockwell
        didn't know in detail how the VIA worked.
     
        (2001-03-31)