18 Mar
2018
18 Mar
'18
7:33 p.m.
From: Paul McJones <paul(a)mcjones.org>
I suspect the CPU architect (Gene Amdahl -- not
exactly a dullard)
intended programmers store array elements at increasing memory
addresses, and reference an array element relative to the address of the
last element plus one. This would allow a single index register (and
there were only three) to be used as the index and the (decreasing)
count.
I suspect the younger members of the list, who've only ever lived in a world
in which one lights ones cigars with mega-gates, so to speak, may be missing
the implication here.
Back when the 704 (a _tube_ machine) was built, a register meant a whole row
of tubes. That's why early machines had few/one register(s).
So being able to double up on what a register did like this was _HYYUUGE_.
Noel