On Sat, Mar 11, 2023 at 12:20 PM, Mark Waterbury wrote:
Having 16 MB of address space total available greatly alleviated many of the
problems that DOS/360 and OS/360 suffered from, with typically less than 512K
of core memory for DOS/360, and less than 1 MB of core for OS/360.
512K? *snort*
DOS/360 could run 16K (1/32 of 512K).
This was
especially troublesome for MVT, where running many jobs with different region
sizes would end up fragmenting whatever small amount of real core memory was
available; and this problem was so bad that it often required an (unplanned)
IPL to "fix" it.
I've read that MVT regions needed four times the region they were expected to need (the working set?); this was also alleviated by the 16M virtual address space.
Of course, once customers grew into (and stressed) their virtual systems with multiple address spaces (MVS & VM), their priority was real storage relief, which is how MVS and VM/HPO with 16 MB virtual addressability got 64 MB real memory on the late 1970's hardware.
Even so, DOS/VS and OS/VS1 and SVS remained quite popular for far longer than I think IBM ever anticipated.
z/DOS lives! (I think it's got a cottage down the beach from Frodo.)
