Re: ARM is sort of channeling the IBM 360

On Thu, 20 Jun 2024 14:28:04 -1000, Lynn Wheeler wrote:

a little over decade ago was asked to track down decision to add virtual
memory to all 370s. basically MVT storage management was so bad that
required specifying region storage requirements four times larger than
used ...

Let me see if I got this straight.

In the early days, the offshoots of OS/360 were “MFT” (“Multiple Fixed
Tasks”) and “MVT” (“Multiple Variable Tasks”). The “Multiple” part had to
do with this new-fangled thing called “multiprogramming”: basically, there
was so much RAM available by that point that you could typically keep
multiple programs memory-resident at once, even if only one was executing,
instead of having to swap everybody but the current program out.

The difference was, with MFT, a program had to declare its memory
requirement before it could be started, and the only way to change that
was to stop the program and start it again. Whereas MVT allowed a program
to change its memory requirements while it was executing. (Whoah! Program
relocation requirement styleee!)

Then, when virtual memory came along, MFT became OS/VS1, while MVT became
OS/VS2.

Eventually, the MFT→OS/VS1 line died a long-overdue death, and OS/VS2
became “MVS”. Not sure what other name changes happened along the way, but
nowadays this is known as “z/OS”.

Does that make sense?