geoffk@belfry.sandiego.NCR.COM (Geoffrey Kim) (03/05/87)
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!
dillon@CORY.BERKELEY.EDU (Matt Dillon) (03/06/87)
The copyprotection designer can basically do anything, since you have direct control overthe flux transitions (the Amiga does the MFM encoding then DMA's the track buffer to the disk). Thus, theoretically, you can do even more then you could through a 'full' disk controller. More and more people are refusing to buy copyprotected software mainly because it ties up a disk drive, masters and even copies can get trashed, and such software is not easily placed on other storage media (hard disk, etc...). Thus, the general industry trend is away from copyprotection and towards large manuals. -Matt
cmcmanis@sun.uucp (Chuck McManis) (03/06/87)
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.