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From: Thomas Koenig <tkoenig@netcologne.de>
Newsgroups: comp.arch
Subject: Re: What is an N-bit machine?
Date: Fri, 29 Nov 2024 19:17:50 -0000 (UTC)
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Anton Ertl <anton@mips.complang.tuwien.ac.at> schrieb:

> In the early 1980s the width of the data bus of the main
> implementation of an architecture was considered to be defining the
> bitness of the architecture.  This is especially noticable in the
> 68000, which was usually described as 16-bit CPU, despite having
> 32-bit address and 32-bit data registers, because it has a 16-bit data
> bus.  I think that even Motorola called it a 16-bit CPU. With low-cost
> variants such as the 8088, the 68008, and later the 386SX, that idea
> was not kept up.

It had been my impression that the width of the ALU was the
definition for many computers - the widest integer that can
natively be handled.  (That does not really fit for the low-end
/360, but that was a 32-bit architecture, and worked for the mid-
and high-end machines).  The 68000 was indeed advertised as a
16-bit processor, the 68008 also had a 16-bit ALU.

The original Nova with its 4-bit ALU does not really fit, I
think Edson de Castro quipped was that it was a 4-bit computer
masquerading as a 16-bit computer. (They later introduced
real 16-bit computers).

Notable counterexamples? (OK, the PDP-8/S :-)