3 Oct
2019
3 Oct
'19
6:50 a.m.
On Oct 2, 2019, at 3:02 PM, Rich Alderson via cctalk
<cctalk at classiccmp.org> wrote:
From: Mark Kahrs
Sent: Tuesday, October 01, 2019 7:24 PM
While we now think of "register" as a specific bit of hardware distinct from
memory, that isn't necessary. The term makes perfect sense as a small set of storage
elements that are treated differently than main memory in the instruction set. For
example, the IBM 1620 has no registers (the ISA only references main memory). Some early
machines, the PDP-6 I believe is an example, have "registers" in the ISA but
they actually correspond to specific parts of main memory. Ditto the Philips PR-8000,
which has 8 sets of 8 registers (one set for each interrupt priority level) actually
implemented in locations 0-63 of main memory.
In a 1948 computer architecture course. Adriaan van Wijngaarden referred to "fast
memory" for what we now call registers; that document in effect is an early
discussion of memory hierarchy.
paul
The first implementation was done for the 7090 by
McCarthy (hence CAR and
CDR --- Contents of Address Register and Contents of Decrement Register).
In the 70x series of IBM scientific systems (704, 709, 7040, 7090, 7044, 7094),
the word "register" referred to memory locations rather than to the
accumulator
or multiplier/quotient. Each memory register was 36 bits long, and could be
treated as 4 fields: A 15 bit address, a 15 bit decrement, a 3 bit tag, and a
3 bit index selector.