bryce@COGSCI.BERKELEY.EDU (Bryce Nesbitt) (05/15/87)
[Re: Reading Mac disks on the Amiga] Sorry to bring this net-worn topic up, but it appears that someone has done it. Well, almost done it: A product called "disk-2-disk" claims to read and ->write<- Commodore 4040/1541/1571 disks on the Amiga using the A1020 5 1/4 drive. The Commodore 5 1/4 inch disks are are similar to Mac disks in many ways: 1> Both use GCR encoding. The methods differ only in the details of the implementation. 2> Both use variable density. The Commodore format takes advantage of the extra area of the outer tracks by increasing the bit-rate electronically. The Mac does the same thing by slowing the motor on the outer tracks. There apparent success may be a result of: 1> Tricky programming. 2> Magic twoggling of Paula. (tsk, tsk.) 3> Magic inherent in the A1020 disk drive. ---------------------------------------- The company making these claims is: [Central Coast Software, 268 Bowie Drive, Los Osos, CA 93402 805-528-4906] I have no connection with this company other than I read their add in The Transactor and said "hey, this may be significant". ----------------------------------------- More technical comments not needed above: The Commodore drives have four distinct "zones". A two bit output register sets the starting point for a counter and thus can change the countdown by 0,1,2 or 3 cycles. The output is used by the bit clock. The Mac speed value is read at intervals out of the sound buffer (!). Unlike the electronic switching used above, the mechanical nature of this approach requires waiting for the drive to stabilize at the new speed. Now out of my depth and working on rumor-> the new Mac+ or Mac SE uses a constant speed drive and manages the changes electronically.
scotty@l5comp.UUCP (Scott Turner) (05/17/87)
In article <8705150540.AA04612@cogsci.berkeley.edu> bryce@COGSCI.BERKELEY.EDU (Bryce Nesbitt) writes: >A product called "disk-2-disk" claims to read and ->write<- Commodore >4040/1541/1571 disks on the Amiga using the A1020 5 1/4 drive. The >Commodore 5 1/4 inch disks are are similar to Mac disks in many ways: >There apparent success may be a result of: > >1> Tricky programming. >2> Magic twoggling of Paula. (tsk, tsk.) >3> Magic inherent in the A1020 disk drive. They use the motor pulsing trick I spoke of. :-) And they are VERY persistant, creative, helpful people. And while I'm talking about Central Coast, if you buy their Dos-2-Dos product make sure you get version 1.5 or greater. Previous versions were rather naive in their handling moving the head around. This has been corrected in 1.5, and I now use this product to move messyDOS stuff Amiga <--> Zenith 181. Works great and my Z-181 has 5.25" capabilities. (If you want messyDOS why not get something out of it you can't get from your Amiga like being a laptop?) Scott Turner -- L5 Computing, the home of Merlin, Arthur, Excalibur and the CRAM. GEnie: JST | UUCP: stride!l5comp!scotty | 12311 Maplewood Ave; Edmonds WA 98020 If Motorola had wanted us to use BPTR's they'd have built in shifts on A regs [ BCPL? Just say *NO*! ] (I don't smoke, send flames to /dev/null)