From Newsgroup: comp.arch
Thomas Koenig <
tkoenig@netcologne.de> wrote:
Tim Rentsch <tr.17687@z991.linuxsc.com> schrieb:
Thomas Koenig <tkoenig@netcologne.de> writes:
I think "ALU can add up to n-bit numbers" is a reasonable definition
for an n-bit architecture, which also fits the 16-bit 68000.
It does not fit the 360/30, or the Nova (but see de Castro's remark
on the latter).
To me, the phrase "n-bit architecture" should depend only on such
characteristics as are defined by the architecture, and not depend
on features of a particular implementation. The 360/30 has a 32-bit
(or is it 64-bit?) architecture, but only an 8-bit implementation.
If I may add a personal note, it's disappointing that postings in a
group nominally devoted to computer architecture routinely ignore
the distinction between architecture and implementation.
I'm well aware of that distinction.
On the other hand, I have right before me a book with the title
"MC68000 16-BIT MICROPROCESSOR User's manual third edition", ISBN 0-13-566695-3 (in paperback). One may argue that the authors
of that book didn't know what they were writing about (since the
68000 has a 32-bit ISA), but I would try to define the terms in
such a way that this is also included.
Marketing.
At the time only mini-computers were 32 bit, which only shipped tens of thousands of computers for tens of thousands of dollars each.
I bought one of the first Macintosh’s which had 128k, which was clearly an inadequate amount of RAM. I looked at building building a fat Mac with 512k
by desoldering the 16 DRAM’s, but those chips at higher density cost $1,000 at the time, half the cost of the Mac.
Took time for DRAM costs to drop, my next machine was MacPlus with 1
megabyte.
Motorola was going for mass market, and mass market could not afford to
fill more than 16 bits of address space. Macintosh was not mass market.
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