Re: ancient disks, Architectural implications of locate mode I/O

According to Stephen Fuld <SFuld@alumni.cmu.edu.invalid>:

Things would have been much better if they simply used some sort of
"table of contents" or index at the start of the PDS, read it in, then
did an in memory search.  Even on small memory machines, if you had a
small sized index block and used something like a B-tree of them, it
would have been faster.

I believe that's what they did with VSAM.

The 360/20's disk controller formatted the disk with 270 byte fixed
length records, no keys.  Nonetheless the IOCS library provided ISAM
with track and cylinder indexes with the keys of the last record on
the track or cylinder.  It would probably have run quite fast if they
had buffered the indexes in core but they didn't since the whole
thing including the application had to fit in 12K or 16K bytes.

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