68K Macs with MacOS 7.5 still in production use...

Chris Hanson cmhanson at eschatologist.net
Mon Sep 12 15:40:56 CDT 2016

On Sep 12, 2016, at 2:21 AM, Peter Corlett <abuse at cabal.org.uk> wrote:
> On Sun, Sep 11, 2016 at 06:43:32PM -0700, Chris Hanson wrote:
>> This person was talking about 680x0-based Macs being “16-bit.” Ugh.
> The original 68000 *was*. Although there were instructions for 32 bit ALU
> operations, it only had a 16 bit ALU and the operands had to go through the ALU
> twice. This illusion went away with multiplication and division, which only
> existed in 16 bit form.
> The 68020 onwards made the CPU fully 32 bit, although various bits of legacy 16
> bit cruft remained for compatibility.

No, the 68000 was a 32-bit CPU, as defined by the register width and programming model.

The fact that it was implemented with a 16-bit ALU and had a 16-bit data path to memory is immaterial.

  -- Chris

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