From: Greg 'groggy' Lehey <grog@lemis.com>
To: Bakul Shah <bakul@iitbombay.org>
Cc: Rudi Blom <rudi.j.blom@gmail.com>, tuhs@tuhs.org
Subject: [TUHS] Sector interleaving (was: Clever code)
Date: Thu, 15 Dec 2022 17:39:03 +1100 [thread overview]
Message-ID: <20221215063902.GC84239@eureka.lemis.com> (raw)
In-Reply-To: <29888CC6-CA23-4361-BC9C-1B8A775C8DA9@iitbombay.org>
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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@gmail.com> wrote:
>>
>> 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!
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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prev parent reply other threads:[~2022-12-15 6:39 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-12-13 3:30 [TUHS] Re: Clever code Rudi Blom
2022-12-13 3:41 ` Warner Losh
2022-12-13 3:53 ` Dave Horsfall
2022-12-13 4:03 ` George Michaelson
2022-12-13 8:05 ` Ralph Corderoy
2022-12-13 9:45 ` Dagobert Michelsen
2022-12-13 7:47 ` Ralph Corderoy
2022-12-13 19:56 ` Dave Horsfall
2022-12-13 11:46 ` John P. Linderman
2022-12-13 14:07 ` Douglas McIlroy
2022-12-13 14:31 ` arnold
2022-12-13 14:48 ` Ralph Corderoy
2022-12-13 15:10 ` Douglas McIlroy
2022-12-13 15:34 ` Stuff Received
2022-12-13 15:56 ` Ralph Corderoy
2022-12-13 23:02 ` Harald Arnesen
2022-12-14 7:31 ` arnold
2022-12-15 18:06 ` Marc Donner
2022-12-15 18:08 ` Marc Donner
2022-12-15 6:30 ` [TUHS] Delay line memory (was: Clever code) Greg 'groggy' Lehey
2022-12-13 15:52 ` [TUHS] Re: Clever code Bakul Shah
2022-12-13 16:14 ` Ralph Corderoy
2022-12-13 16:30 ` Bakul Shah
2022-12-15 6:39 ` Greg 'groggy' Lehey [this message]
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