19 Nov
2009
19 Nov
'09
7:20 p.m.
On 19 Nov 2009 at 10:39, Russ Bartlett wrote:
The model 20 was the smallest and used a reduced
instruction set.? The
programming language of choice was RPG (not RPG II).?? Those familiar
with the Univac range 9200, 9300, 9400 (also used IBM 360 instruction
set) will know that the Univac 9200 pretty well mirrored the IBM
360/20.? Never heard of a model 7 though.
For all intents and purposes, the Model 20 was a completely different
machine. Not binary-compatible with its bigger siblings; used
halfword registers. A 360/30 programmer might start his program with
"BALR 15,0" to establish an addressing base through register 15, but
the 360/20 programmer would write "BASR 15,0".
The bulk of instructions on the Model 20 were memory-to-memory,
including packed decimal arithmetic. It's noteworthy that there was
a packed decimal multiply instruction, but no binary register-based
multiply, for example.
There was also a model 25, which was much closer to the standard line
(model 30 and up), but it came along rather late in the series. A
lot of model 20's went to installations to replace unit-record
equipment, rather than another computer.
Peripherals for the 20 were less than wonderful. In particular, I
remember the "Mother Fletcher's Card Mulcher" (cleaned up for general
consumption)...
--Chuck