On 3/10/23 13:00, Paul Koning via cctalk wrote:

On Mar 10, 2023, at 1:38 PM, Chuck Guzis via cctalk <cctalk@classiccmp.org> 
wrote:

On 3/10/23 10:20, Bill Gunshannon via cctalk wrote:

The first mainframe I worked on was single user, single tasking.
S/360 DOS provided for one "background" memory partition and two
"foreground" ones.  Batch submissions would be background, with some
installations using the smaller foreground ones for interactive use.
You mean DOS/360 as opposed to OS/360?  I don't know that one.  But OS/360 came 
in three flavors: PCP, MFS, and MVS.

MFT was Multiprogramming with a Fixed number of Tasks, MVT was Multiprogramming with a Variable number of Tasks.  MFT had "fixed" partitions, although the operator could "drain" partitions and then rearrange them manually.  MVT automatically rearranged partitions by looking at the memory requirements of the next-up programs in the queue.  Well, that all sounds great, except that allowing the user to ask for completely random partition sizes ended up filling memory with little chunks of odd-size partitions that left memory fragmented.  So, the fix was to only allow partition sizes in some standard quanta like 50 K.  If you asked for 37 K you would run in a 50K partition and be charged for it. MVS was a 370 OS.

Jon

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