As mentioned I am moving my office/shop into another room. And stumbled over a manual of my first commercial product, a cash register written in MF COBOL for PC's. And some other documents from IBM for the System 360, the one I learned COBOL on.
That one was worn out pretty much and not readable anymore. So I googled for it. What a time travel. And there I stumbled over it. The 360 had a supervisor mode and thus a supervisor program, written by IBM. But a 370 had no 'user' programming it. It had a programmer programming the solution for a problem of the future user.
The 'problem program' written by the 'problem programmer'. Consistend thru 299 pages written in 1964. How far sighted!
Yeah, that was IBM at its best, moving from 4 different architectures with different instruction sets and different compilers/assemblers to ONE instruction set on all 6 different machines they presented on the same day. The system 360.
Sure that instruction set got extended over the years, but all instructions of the 360 set are still in the newest Z-series. You can still run 360 programs unmodified on a new Z. Eat that Intel.
Actuall a quite interesting instruction set. Lots of fun in there. Privilegded instructions, relocation of programs and data in memory thru Base registers, memory protection of 2048 byte blocks with a 4bit key that needs to match to the key in the program, else access violation. Same for I/O. Protected by key, running over a channel to a dedicated subsystem with its own processor and program.