After leaving Amdahl I worked for a while in Electronic Design Automation. One year at the IEEE Design Automation Conference I met a random person at a happy hour who was an ex-IBM OS programmer. He said that he once spent a year rewriting a part of the OS to use a particular instruction entirely because “Amdahl didn’t have it yet.” Says I: “When was this?” ... “Ah, at that time part of my job was adding that instruction to the Amdahl CPU.”
The conversation felt like an old Mad Magazine “Spy vs. Spy” cartoon. We were both bemused.
Around 2012(?), working for another major bank, I was asked to make an enhancement to a funds transfer system written in assembler, as no one else left in the pool of programmers had any experience. I had to dig out my old text book which I luckily found, and my old yellow card, and relearned enough to make the change.
(I think there might have been one or two other supervisor mode-instructions, but there were weirdos like "stop the other processor", for example).
When I started mainframe programming, I was given a pocket-sized 'yellow card' that listed all the machine instructions and arguments. It was invaluable for dump-reading.
My co-workers (who were all older when I started) had similar cards, except in different colors. There were white, pink and green cards, too. You could tell when somebody started programming by the color of their card.
I kept mine, still have it.
>BYTE criticized The Adolescence of P-1 for what it stated were unrealistic expectations for an artificial intelligence running on 1970s IBM mainframes. It suggested that the author could have set the novel in the 1990s and use fictional future IBM computers to make the plot more plausible.
Also check out the OS/390 ADCD Redbook:
Which I found pretty helpful for finding my way around. (I see from the cover that it includes MP3000 info!)
Edit: Have you seen this? (I think this guy hangs out on HN)
And along similar lines, it's kind of fun, if not at all useful in any economically rational sense of the term, to write nontrivial source- and binary-compatible code that builds and runs on everything from a 40-year-old 370 to a current-model Z (speaking hypothetically, as I don't actually have access to even a reasonable facsimile of the latter; I have, however, tested as far forward as late-model OS/390 running in 64-bit z/Arch mode on emulated hardware).
More or less until the IBM PC, it was normal for computer vendors to supply a detailed bit-level breakdown of instructions, memory operation, data formats, interrupt structure, and so on.
IBM supplied hardware schematics and microcode listings for their S/370 hardware. They were in the machine room and freely available for perusal by us.
In a bit of irony, they also supplied schematics and microcode for the Itel clone. That's because the Itel was a true clone. It was designed by copying IBM's circuitry, but implemented in Motorola 10K series ECL instead of IBM's proprietary technology.
You read that right. In order to debug a problem with the Itel, the Itel field service engineers used IBM's schematics.
I think a lot of this free availability was because IBM was facing antitrust pressure from the US government. I don't know all the details.
Here's more history about the clone: http://www.silogic.com/NAS/NAS.html