----------------------------------<snip>----------------------------
there use to be some technology laying out data records on 3330
cylinders with "dummy" spacer records that would allow for channel
program processing latency to do a head switch operation (on the same
cylincer) between the end of a data record (on one track) and the start
of the (next) data record (on another track) ... without a rotational
miss. Several 370s; 145, 148, & 168, the channel processing was fast
enough to execute the head-switch in the time it took a 3330 disk to
rotate the dummy spacer record amount.
The problem was that 158 channels had higher latency and would only make
the head-switch (w/o a miss & additional revolution) 20-30% of the time
(the rest of the time, the head-switch would miss picking the next
record and have to may a complete revolution before trying again). The
3330 track size wasn't large enuf to make the dummy record sizes larger
(using 4k data records). It turned out that the same rotational miss
rates was true for the 303x channel directors (regardless of the machine
they were attached to; since they all used the same 158 integrated
channel processing).
--------------------------------<unsnip>----------------------------
We called them "Gap Records" at NCSS and they worked very well for
paging on 2305 devices. We'd use the first exposure for the first page,
the second exposure for the third page and so on. They were connected to
a 370/168 via 2860 Selector Channels. Grant Tegtmeier designed the code
and computed the sizes of the Gap Records. He also installed 3330 and
2305 support code, of his own design, in our modified CP67/CMS system.
In a long weekend! He was noted for long periods of seeming boredom,
punctuated by spurts of sheer genius.
--
Rick
--
Remember that if you’re not the lead dog, the view never changes.
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