From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on inbox.vuxu.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=5.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,RCVD_IN_DNSWL_NONE autolearn=ham autolearn_force=no version=3.4.2 Received: from minnie.tuhs.org (minnie.tuhs.org [45.79.103.53]) by inbox.vuxu.org (OpenSMTPD) with ESMTP id 74a71c48 for ; Wed, 9 Jan 2019 15:10:37 +0000 (UTC) Received: by minnie.tuhs.org (Postfix, from userid 112) id 503EBA35D5; Thu, 10 Jan 2019 01:10:36 +1000 (AEST) Received: from minnie.tuhs.org (localhost [127.0.0.1]) by minnie.tuhs.org (Postfix) with ESMTP id 72187A35C4; Thu, 10 Jan 2019 01:10:13 +1000 (AEST) Received: by minnie.tuhs.org (Postfix, from userid 112) id 84616A35C4; Thu, 10 Jan 2019 01:10:10 +1000 (AEST) Received: from mail.bitblocks.com (ns1.bitblocks.com [173.228.5.8]) by minnie.tuhs.org (Postfix) with ESMTP id 2687BA35B7 for ; Thu, 10 Jan 2019 01:10:10 +1000 (AEST) Received: from bitblocks.com (localhost [127.0.0.1]) by mail.bitblocks.com (Postfix) with ESMTP id E94D2156E41B; Wed, 9 Jan 2019 07:09:55 -0800 (PST) From: Bakul Shah To: Warner Losh In-reply-to: Your message of "Tue, 08 Jan 2019 22:45:31 -0700." References: <966501A7-7736-4EB0-841A-C1516C876272@quintile.net> <20190109052004.9DB6F156E410@mail.bitblocks.com> Comments: In-reply-to Warner Losh message dated "Tue, 08 Jan 2019 22:45:31 -0700." MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <65457.1547046595.1@bitblocks.com> Date: Wed, 09 Jan 2019 07:09:55 -0800 Message-Id: <20190109151002.E94D2156E41B@mail.bitblocks.com> Subject: Re: [TUHS] TUHS Digest, Vol 38, Issue 10 X-BeenThere: tuhs@minnie.tuhs.org X-Mailman-Version: 2.1.26 Precedence: list List-Id: The Unix Heritage Society mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: The Eunuchs Hysterical Society Errors-To: tuhs-bounces@minnie.tuhs.org Sender: "TUHS" On Tue, 08 Jan 2019 22:45:31 -0700 Warner Losh wrote: > > > > > For example, I could envisage a disk where the sectors are deliberately > > > not numbered sequentially i.e. they've taken rotational latency into > > > account for you? > > > > We did in fact use an interleave factor of more than 1 (skip > > more than 1 block for consecutively numbered sectors) to > > improve throughput but that had to do with slow processing. > > We did discuss "dead reckoning" (invoking the service routine > > right when the N+1 numbered sector was near the r/w heads) but > > I don't think we implemented it. > > > > For floppy drivers that I've seen the source to in early unixes, this was > often the case. One minor device would be to access the 'raw' device, while > another would be to access the 'cooked' sector numbers where the mapping > was anything but linear. you'd have an interleave of, say, 4 or so, and > then a 'slip' from track to track. The interleave factor was based on how We used interleaving on the hard disk because a 5Mbps ST412 drive could stream data faster than typical user program could handle (on a 5.6Mhz bus machine). We used h/w support as the machine was already too slow to do any s/w interleaving! Example: for an interleave of 1, at the time formatting the disk, sector ids would be written in this sequence: 1 8 2 9 3 A 4 B 5 C 6 D 7 E We picked the interleave number based on some typical use cases at the time. The floppy driver was was a completely separate driver for various reasons.