Drums

[Peter Flass]

A discussion of IBM drums on Wikipedia started me thinking - I always
associated drums with use for paging, but what would they have been used
for on 360’s other than the /67? Would people put parts of the OS on them,
use them for rollout/rollin, or what?

[Anne & Lynn Wheeler]

Post by Peter Flass
A discussion of IBM drums on Wikipedia started me thinking - I always
associated drums with use for paging, but what would they have been
used for on 360’s other than the /67? Would people put parts of the OS
on them, use them for rollout/rollin, or what?

univ. had 2301 "drum" (something of 2303 "drum" ... except read/write
four tracks in parallel, 1/4th the number of tracks each four times
larger and four times the transfer rate) for 360/67 supposedly for
tss/360. Was used for sys1.svclib when running as 360/65 with os/360
(some discussion in the DIAG thread ... os/360 did enormous number of
disk i/o for job step supervisor as well as file open/close SVCs
... file open&close SVCs had enormous of number of sys1.svclib modules
that had to be dragged sequentially through the os/360 svc transient
area.

when univ finally decided that wasn't ever going to get tss/360 running
production ... the univ. returned the 2301. the was some sort of
univ/ibm blowup and I was given overnight to redo os/360 systen with
sys1.svclib on 2314. Afterwards I escalated and said that was no way to
run a datacenter and in the future I wanted advanced notice for
configuration changes.

before it was returned, cp67/cms was installed at univ (before 2301
removed) and got to play with it on weekends ... original CP67 paging
code did FIFO single page i/o per channel program ... peaked around
80/sec. I rewrote the code to do multiple transfer per channel program
ordered to do maximum transfers per revolution and could peak close to
channel speed 270/sec. Also did disk FIFO queued requests, I redid for
ordered seek for all channel programs and chaining page transfers for
same cylinder (arm position) in single channel program (again attempting
to maximize transfer per revolution).