Re: What is an N-bit machine?

On Thu, 1 Jan 1970 0:00:00 +0000, John Dallman wrote:

In early computer designs, arithmetic registers were much longer than
addresses, the classic examples being machines with 36-bit words and 15-
to 18-bit addresses.
>
Large logical address spaces started with the IBM 360, which had 32-bit
arithmetic registers and 32-bit address registers. You couldn't put
32-bits worth of physical memory in a machine for over a decade after it
appeared, but it was allowed for in the architecture.

Until 360/67, the address space was limited to 24 bits. With 360/67
it jumped to 32-bits, only to retreat to 31-bits for the life of 370.

Nowadays, the bit-ness of a machine seems to be the *smaller* of the
arithmetic registers and the address space.

The bitness of a machine has lost all significance when one includes
512-bit SIMD registers.
And we may be approaching a day where we end up with more address space
that bits in an address register !!?