From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S263415AbTDYRhc (ORCPT ); Fri, 25 Apr 2003 13:37:32 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S263459AbTDYRhc (ORCPT ); Fri, 25 Apr 2003 13:37:32 -0400 Received: from turing-police.cc.vt.edu ([128.173.14.107]:50049 "EHLO turing-police.cc.vt.edu") by vger.kernel.org with ESMTP id S263415AbTDYRha (ORCPT ); Fri, 25 Apr 2003 13:37:30 -0400 Message-Id: <200304251748.h3PHmjQd012895@turing-police.cc.vt.edu> X-Mailer: exmh version 2.6.3 04/04/2003 with nmh-1.0.4+dev To: root@chaos.analogic.com Cc: Linux Kernel Mailing List Subject: Re: versioned filesystems in linux (was Re: kernel support for In-Reply-To: Your message of "Fri, 25 Apr 2003 13:06:18 EDT." From: Valdis.Kletnieks@vt.edu References: <200304251618.h3PGINWP001520@81-2-122-30.bradfords.org.uk> Mime-Version: 1.0 Content-Type: multipart/signed; boundary="==_Exmh_200861245P"; micalg=pgp-sha1; protocol="application/pgp-signature" Content-Transfer-Encoding: 7bit Date: Fri, 25 Apr 2003 13:48:39 -0400 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org --==_Exmh_200861245P Content-Type: text/plain; charset=us-ascii On Fri, 25 Apr 2003 13:06:18 EDT, "Richard B. Johnson" said: > On Fri, 25 Apr 2003, John Bradford wrote: > > Just wondering how difficult it would be to make a 9-track tape drive > > from scratch, and connect it up to the parallel port... Do you think > > that old hard disk motors, from 5.25" MFM disks be powerful enough for > > the 120IPS tape transport? > > > > John. > > The disk-drive motors, even for the 5.25 floppies were pancake motors > designed to directly turn the floppy, or run a belt with a small > ratio. You need a motor that runs at relatively high speed to turn the > capstan. If the capstan was 1 inch in circumference (about 0.2'' in > diameter), you need 120 revs/sec = 7200 r.p.m. You won't do this with > a floppy motor. It's not that bad, actually - the capstan is more like 4 inches across, and the minimum actual diameter of the tape is about 6 inches, giving a circumference of 18" so you only need about 400RPM at the "empty" reel and maybe half that at the "full" reel. (More than you ever wanted to know about old tape drives, probably ;) Of bigger concern is that the inter-block gap is only 0.5 (or maybe 0.75 inches, the memories are dim ;) - and you need to be able to stop and then get back up to speed in that distance (or decelerate, rewind, and get a running start). This was why the IBM3420 (and predecessor) tape drives had vacuum columns - there'd be a loop of up to 5-6 feet in a column on each side of the head. To move the tape for a single block, it would increase suction on one column, causing the tape to be pulled in, and reduce it in the other, feeding tape out. Since the weight of the 6-10 feet of tape being moved is low, acceleration is quite fast - a 3420 doesn't stream continuously, and it's QUITE possible to be writing short blocks (80 bytes or so at 6250 bytes per inch, which results in an actual block of about half an inch) where the tape stops, accelerates, writes, stops, etc.. and still maintain 200 inches per second throughput (yes, the vacuum columns ARE emitting a 200hz square wave sound when you do this - programs have been done to play music by using different block sizes...) The actual capstans would then have several foot of buffering to get up to speed (or stop), which was needed as the rotational inertia of a full 2400 foot 9 track tape is *not* trivial. Low-end 9-track transports did a cheaper version of this, using 2 tension arms and a drive motor near the head, similar to audiophile reel-to-reel tape transports. --==_Exmh_200861245P Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.1 (GNU/Linux) Comment: Exmh version 2.5 07/13/2001 iD8DBQE+qXT3cC3lWbTT17ARAqwzAKC0NZ3Tth9V6QN0/+Dusa65j7ND4ACfSCqq ofwyH2aWRlXjXimYISon1NM= =Lp3k -----END PGP SIGNATURE----- --==_Exmh_200861245P--