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

Jecel Assumpcao Jr. jecel at
Fri Sep 16 17:15:53 CDT 2016

The 68000 has three separate 16 bit ALUs: one for DataLow, one for
AddressLow and another for AdressHigh. DataHigh can be processed by
either the first or the second one. The first one implements all
operations while the other two only do add/subtract and some limited

See figure 8 of:

So the 68000 can process 48 bits at a time, but nobody every called it a
48 bit architecture :-)

Many official Motorola documents and articles did call it a 16 bit
processor, but others said it was a 32 bit one. Certainly the Motorola
engineers I dealt with in 1982 always considered it a 32 bit
architecture and Apple was hardly the only one to use that term in its
marketing material (see Atari, Commodore, Sun, etc).

-- Jecel

More information about the cctalk mailing list