Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!seismo!lll-lcc!styx!ames!ucbcad!ucbvax!decvax!decwrl!sun!cmcmanis From: cmcmanis@sun.uucp (Chuck McManis) Newsgroups: comp.sys.amiga Subject: Re: Copy Protection on Amiga format disks Message-ID: <14598@sun.uucp> Date: Fri, 6-Mar-87 12:34:02 EST Article-I.D.: sun.14598 Posted: Fri Mar 6 12:34:02 1987 Date-Received: Sun, 8-Mar-87 09:59:25 EST References: <121@belfry.sandiego.NCR.COM> Organization: Sun Microsystems, Inc. - Mtn View, CA Lines: 36 Keywords: Copy Protection on Amigas Summary: CBM uses sectors but you can still play games with the tracks In article <121@belfry.sandiego.NCR.COM>, Geoffrey Kim writes: > In previous articles dealing with disk format questions it was > mentioned that the Amiga does not use sectors on its tracks, but > writes out entire tracks at a time. I am new to the Amiga > scene and was wondering how various copy protection schemes were > implemented. I know most of the popular methods on the IBM PC > software (e.g. short sectors, 1 sector per track, half-tracking, > spiral tracking, synchronized inter-sector gaps, CRC and parity > errors.) However, almost all these schemes are based upon sector > orientation. Does the Amiga employ the same techniques, but on > a track basis? Enquiring minds want to know! > The Amiga does read and write full tracks however it divides those tracks into sectors of 512 bytes each. Programatically the disk appears as a series of blocks from (0+Reserved) to (Max) where the number of reserved blocks and the Max blocks are specified by the device. When reading and writing tracks the user program can call the trackdisk device directly and put anything it wants to in the track buffer. That means it can put is bogus data, or even a bad track. Unfortunately if AmigaDOS ever trys to validate the disk it fails (because of the bad area) and the disk is marked as unreadable. The way to prevent AmigaDOS from attempting to read the bad block or track is not have it present in any file, unfortunately if you write to the disk there is a measurable chance that AmigaDOS will use that area for the new file and that too will blow up the CP. The answer is of course not to copy protect the program, however for those applications where it is not possible to sell it unprotected the best bet is a cleverly selfmodifing program that converts itself from a demo to working program after checking that it hadn't been copied. -- --Chuck McManis uucp: {anywhere}!sun!cmcmanis BIX: cmcmanis ARPAnet: cmcmanis@sun.com These opinions are my own and no one elses, but you knew that didn't you.