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From: Terje Mathisen <terje.mathisen@tmsw.no>
Newsgroups: comp.arch
Subject: Re: Byte Addressability And Beyond
Date: Thu, 2 May 2024 09:54:49 +0200
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MitchAlsup1 wrote:
> Lawrence D'Oliveiro wrote:
>=20
>> Byte addressing was invented by IBM for the System/360, introduced in =

>> 1964. At least as I understand it. Up to that time, and indeed for a=20
>> long time after, machines had a =C3=A2=E2=82=AC=C5=93word length=C3=A2=
=E2=82=AC=C2=9D which was the=20
>> smallest addressable unit of memory. This could have a range of sizes,=
=20
>> e.g.
>=20
>> =C2=A0=C2=A0=C2=A0 12 -- DEC PDP-5/8
>> =C2=A0=C2=A0=C2=A0 18 -- DEC PDP-1/4/7/9
>> =C2=A0=C2=A0=C2=A0 36 -- DEC PDP-6/10
>> =C2=A0=C2=A0=C2=A0 60 -- CDC 6000-series
>> =C2=A0=C2=A0=C2=A0 64 -- Cray
>=20
> CDC had a number of machines with 12-bit times k words. k element {1,2,=
3,5}
>=20
>> I=C3=A2=E2=82=AC=E2=84=A2m sure there were also 24- and 48-bit machine=
s. Note the=20
>> popularity of numbers with a range of different integer divisors,=20
>> including powers of both 2 and 3. The byte-addressable machines=20
>> chucked away everything other than powers of 2, which was a step=20
>> backwards in this respect. ;)
>=20
> I would make the argument that 2^k was a step forward not backwards.
> Perhaps another day...

I've seen the argument that e is the best base from an energy=20
standpoint, with 2 and 3 being the two closest integer values.

Working with trits, encoded as -/0/+, would have been feasible, but=20
binary provided much easier implementation. Base conversions are a bit=20
messier when you use base3 as the machine representation, but you could=20
have used 5 trits (243) to handle the US ASCII character set.

In retrospect I'm glad they decided on binary!

Terje

--=20
- <Terje.Mathisen at tmsw.no>
"almost all programming can be viewed as an exercise in caching"