25 May
2016
25 May
'16
6:50 a.m.
On May 24, 2016, at 10:05 PM, Jon Elson <elson at
pico-systems.com> wrote:
On 05/24/2016 02:13 PM, Chuck Guzis wrote:
The 360 model 44, with the emulation option, is somewhat similar. The base machine had a
trimmed down instruction set, shades of microVAX: no decimal or string operations. So you
could not run OS/360. Instead, you had to run PS/44 (or some such name).
Alternatively, you could get the emulation option. That added some extra memory and an
emulation mode, where reserved instructions would trap to the emulator and get emulated
there. So now you could run OS/360, and PL/I or COBOL applications (albeit quite
slowly).
The emulator was loaded, on those rare occasions where the memory got wiped, using the
"Emulator IPL" button, from a binary card deck. That deck was pretty slick: it
was a channel program loop. No CPU code involved at all; the first card was a 4 (?) entry
channel program that would read the remaining cards, which were a standard assembler
output (object deck). Self modifying channel code: since each object card contained the
address and length for its data, the channel program would pick up those two fields and
drop them into the third channel command, which would transfer that number of bytes to
that address.
paul
I seem to recall that reworking the 360/30
microprogramming was preferred by tinkerers over the 360/40 was primarily that CROS was
easier to work with than TROS. I don't recall what the RCA Spectrolas used.
And
the 360/25 had all writeable control store. The control store was just the top 16 KB of
main core memory! To change emulators, restore from a microprogram crash, etc. you loaded
the emulator from a card deck!