15 Dec
2022
15 Dec
'22
6:39 a.m.
On Tuesday, 13 December 2022 at 7:52:49 -0800, Bakul Shah wrote:
On Dec 12, 2022, at 7:30 PM, Rudi Blom
<rudi.j.blom(a)gmail.com> wrote:
CP/M did something similar with floppy disks. It imposed a 6 fold
software interleave between sectors (logical sectors 1, 2, 3.. were
"physical" sectors 1, 7, 13...)
On soft-sectored floppies, the "physical" sectors were really just the
numbers in the sector header. By the time I got involved, computers
were far fast enough that they spent a lot of time just waiting for
the next sector. I wrote a format program that positioned the
"physical" sectors so that there was only one sector between
"physical" 1, 7, 13 and so. It made an amazing difference to the disk
speed.
Greg
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I vaguely remember having read here about 'clever code' which took
into account the time a magnetic drum needed to rotate in order to
optimise access.
Similar consideration applied in the early days of unix workstations.
Fortune 32:16 was a 5.6Mhz machine and couldn't process 1020KB/sec
(17 sectors/track of early ST412/ST506 disks) fast enough. As Warner
said, one dealt with it by formatting the disk so that the logical
blocks N & N+1 (from the OS PoV) were physically more than 1 sector
apart. No clever coding needed!