No interest in OS/VS2 MVS, but I do have OS/2 Warp 4 running in a VM under Oracle VB here on my Win 10 Pro X64 system? I spent the last 10-12 years working on OS/2. I emigrated from Cold, snowy Poughkeepsie to warm, lovely Boca Raton. Best move I ever made, then they went and closed the place and sent us to Austin, Tx. Still not bad as it was mostly warm and only one ice storm a year.
I was stuck on the "big iron" machines the entire time I was working for companies, so I had the luxury of dealing with the top end of both the 360 and 370 series of systems (and the 7094 that overlapped the 360 series introduction.) My experience with the mainframe OS history was like this:
The first 360's ran PCP (Primary Control Program) which was like the original PC DOS system - it ran one job at a time, period. Programs were limited by the size of real memory, so IBM developed the concept of Overlays. These were logical memory spaces that you could swap in and out of physical memory as needed. There were 4 separate overlay "regions" where you could specify the locations of your program's subroutines. The idea was to group the routines so that you could swap regions in and out based on what your program was doing, thus ensuring that the necessary routines were always in physical memory when they were needed.
When memory sizes got bigger (like the Mod 50's and up) IBM came out with MFT (Multiprogramming with Fixed Number of Tasks.) MFT required specifying the size and number of "partitions" that would run tasks simultaneously on the system; each partition had a fixed memory size and of course all the partitions together had to be smaller than physical memory. MFT was a big deal at the time because the machine was able to process instructions for job B while job A was waiting on I/O. This greatly improved productivity.
MVT (Multiprogramming with a Variable number of Tasks) eliminated the requirement to divide physical memory into set partitions. It basically handled memory allocation dynamically, based on the number of concurrent jobs on the system. That number was controlled by the system operators who could start and stop "Initiators"; each Initiator would create it's own dynamically sized partition and would run jobs one after another.
The big change happened when IBM developed the DAT box (Dynamic Address Translation), which was an add-on hardware feature that enabled the concept of virtual memory. This allowed programmers to develop applications that used up to 16MB of virtual RAM, regardless of how much physical memory the program actually had. Needless to say virtual memory changed the entire nature of software development forever.
My first job out of school was in a shop running OS/VS1 (virtual storage version of OS/MFT). I loved every minute of it; so much to learn, and I didn't mind that my "terminal" was a coding pad and an IBM 029 keypunch machine. Egads. Then went to a DOS/VS shop in which I was miserable; DOS seemed so backwards. Then back to OS/VS1, then back to DOS (we bounced around a lot back then, didn't we?). Then we made the leap from DOS/VS to MVS/SP...it was like entering the 20th century. Management said we'd never do it but we did. Then to MVS/ESA (31 bits!), OS/390 and finally to z/OS (64 bits!). People still scoff at the mainframe but its the most stable platform in my company. No "we have to reboot the servers" or "we have to restart the JVMs" to fix problems...it just runs. Unfortunately, it's not a sexy platform and isn't attracting any young talent.
Rob
Quote