> On May 24, 2016, at 10:05 PM, Jon Elson <el...@pico-systems.com> wrote:
>
> On 05/24/2016 02:13 PM, Chuck Guzis wrote:
>> 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!
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
