From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on inbox.vuxu.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=5.0 tests=MAILING_LIST_MULTI autolearn=ham autolearn_force=no version=3.4.4 Received: (qmail 32632 invoked from network); 15 Dec 2022 06:39:43 -0000 Received: from minnie.tuhs.org (50.116.15.146) by inbox.vuxu.org with ESMTPUTF8; 15 Dec 2022 06:39:43 -0000 Received: from minnie.tuhs.org (localhost [IPv6:::1]) by minnie.tuhs.org (Postfix) with ESMTP id BD8174247D; Thu, 15 Dec 2022 16:39:07 +1000 (AEST) Received: from lax.lemis.com (www.lemis.com [45.32.70.18]) by minnie.tuhs.org (Postfix) with ESMTP id 10EB542478 for ; Thu, 15 Dec 2022 16:39:04 +1000 (AEST) Received: from eureka.lemis.com (121-200-11-253.79c80b.mel.nbn.aussiebb.net [121.200.11.253]) by lax.lemis.com (Postfix) with ESMTP id B5A8A28093; Thu, 15 Dec 2022 06:39:03 +0000 (UTC) Received: by eureka.lemis.com (Postfix, from userid 1004) id 076352635BD; Thu, 15 Dec 2022 17:39:03 +1100 (AEDT) Date: Thu, 15 Dec 2022 17:39:03 +1100 From: Greg 'groggy' Lehey To: Bakul Shah Message-ID: <20221215063902.GC84239@eureka.lemis.com> References: <29888CC6-CA23-4361-BC9C-1B8A775C8DA9@iitbombay.org> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="R+My9LyyhiUvIEro" Content-Disposition: inline In-Reply-To: <29888CC6-CA23-4361-BC9C-1B8A775C8DA9@iitbombay.org> Organization: LEMIS, 29 Stones Road, Dereel, VIC, Australia Phone: +61-3-5309-0418 Mobile: +61-490-494-038. Use only as instructed. WWW-Home-Page: http://www.lemis.com/grog X-PGP-Fingerprint: 9A1B 8202 BCCE B846 F92F 09AC 22E6 F290 507A 4223 User-Agent: Mutt/1.6.1 (2016-04-27) Message-ID-Hash: J74FWEJUHKJLSLYTMLSWEJ7WL7N7Y3BF X-Message-ID-Hash: J74FWEJUHKJLSLYTMLSWEJ7WL7N7Y3BF X-MailFrom: grog@lemis.com X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation; header-match-tuhs.tuhs.org-0; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header CC: Rudi Blom , tuhs@tuhs.org X-Mailman-Version: 3.3.6b1 Precedence: list Subject: [TUHS] Sector interleaving (was: Clever code) List-Id: The Unix Heritage Society mailing list Archived-At: List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: --R+My9LyyhiUvIEro Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Tuesday, 13 December 2022 at 7:52:49 -0800, Bakul Shah wrote: > On Dec 12, 2022, at 7:30 PM, Rudi Blom 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 -- Sent from my desktop computer. Finger grog@lemis.com for PGP public key. See complete headers for address and phone numbers. This message is digitally signed. If your Microsoft mail program reports problems, please read http://lemis.com/broken-MUA.php --R+My9LyyhiUvIEro Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iEYEARECAAYFAmOawQYACgkQIubykFB6QiNPnQCfX3PN6LWnDE4RyZwwOCVqfAzs 0GEAn2q5ZZgQrA+3mvVy1BbHgAuuHWF8 =47B2 -----END PGP SIGNATURE----- --R+My9LyyhiUvIEro--