Meaning of "architecture width" - Re: 68K Macs with MacOS 7.5 still in production use...

Eric Smith spacewar at
Sat Sep 17 11:23:45 CDT 2016

On Fri, Sep 16, 2016 at 5:41 PM, Chuck Guzis <cclist at> wrote:
> The TMS9900 has already been identified as a 16-bit ISA, even with its
> bit-serial ALU.

I don't know what the width of the TMS9900 ALU is, but I'm pretty sure
it's not bit-serial, as an add instruction only takes 14 clock cycles,
including four memory cycles. I'd be very surprised if the ALU isn't
either 8 or 16 bits, though 4 might be possible.

Possibly someone is confused by the bit-serial "CRU' I/O space, but
that is unrelated to the ALU width.

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