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

Toby Thain toby at
Thu Sep 15 16:57:10 CDT 2016

On 2016-09-15 2:38 PM, Noel Chiappa wrote:
>     > From: Chuck Guzis
>     > Call it anything you want, but we know what Motorola called it.
> The _first implementation_ may have been 16-bit, but I am in no doubt
> whatsover (having written a lot of assembler code for the 68K family)
> that the _architecture_ was 32-bit:
> - 32-bit registers
> - many operations (arithmetical, logical, etc) defined for that length
> - 32-bit addresses

GPR width, being the visible programmer model, is the most common and 
convenient definition of "architecture" I've come across. But there's no 
reason we can't just say the *visible* architecture is 32 bit (which it 
is), but the "internal" architecture is sort of 16.

Why not have two concepts? They're free. Gordon Bell probably laid this 
out somewhere. Or Blaauw and Brooks.


> Etc, etc, etc, etc.
> 	Noel

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