From owner-freebsd-hackers Mon Apr 24 19:39:44 1995 Return-Path: hackers-owner Received: (from majordom@localhost) by freefall.cdrom.com (8.6.10/8.6.6) id TAA07193 for hackers-outgoing; Mon, 24 Apr 1995 19:39:44 -0700 Received: from ast.com (irvine.ast.com [165.164.128.2]) by freefall.cdrom.com (8.6.10/8.6.6) with SMTP id TAA07178 for ; Mon, 24 Apr 1995 19:39:41 -0700 Received: from trsvax.fw.ast.com (fw.ast.com) by ast.com with SMTP id AA04927 (5.67b/IDA-1.5 for freebsd-hackers@freefall.cdrom.com); Mon, 24 Apr 1995 19:43:25 -0700 Received: by trsvax.fw.ast.com (/\=-/\ Smail3.1.18.1 #18.1) id ; Mon, 24 Apr 95 21:39 CDT Received: by nemesis.lonestar.org (Smail3.1.27.1 #18) id m0s3ZdD-0004vvC; Mon, 24 Apr 95 20:41 CDT Message-Id: Date: Mon, 24 Apr 95 20:41 CDT To: freebsd-hackers@freefall.cdrom.com From: uhclem@nemesis.lonestar.org (Frank Durda IV) Sent: Mon Apr 24 1995, 20:41:38 CDT Subject: Re: Interesting SCSI cdrom problem.. Sender: hackers-owner@FreeBSD.org Precedence: bulk [1]From: Peter da Silva [1]If there is a guaranteed unique ID you can get from the CDROM, you can [1]use that to maintain multiple mount structures in memory, and prompt the [1]user for the appropriate disc when necessary. [1] [1]If the prompt is vectored through a program (and it would pretty much have [1]to be), you could use that to control a jukebox as well. CDs have a field for the UPC data, which should be unique. However there are two problems (at least): 1. Not everybody fills in the field, including many big record companies. (Usually its because the UPC hasn't been assigned by the time the disc is mastered or they get in a hurry, it was dark, etc.) Write-once discs almost never have a valid UPC field and some of the mastering software doesn't even give you the chance to fill it in. 2. Not all CD-ROM drives (including SCSI models) implement a command that delivers the UPC field. That is probably why the CD-DA (audio) player app that Microsoft ships used to read the length information for each track from the TOC and create a hash from it. That was then used to "recognize" the disc being re-inserted so that it could recall preferences, tracks-to-skip, etc. This scheme is reasonably foolproof, providing the disc isn't remastered by a different vendor who gets the timing different on any track on the disc AND there isn't another disc that has the same number of tracks and length. Frank Durda IV |"Where do you want to go today? or uhclem%nemesis@fw.ast.com (Fastest Route)| Wherever Microsoft tells you ...letni!rwsys!nemesis!uhclem | to." - TM (C) 1994 Madsoft. ...decvax!fw.ast.com!nemesis!uhclem |