leblanc@eecg.toronto.edu (Marcel LeBlanc) (11/10/88)
[] Can somebody tell me if Amigas, IBMs, 1581s (CBM 8-bit), and Ataris use a compatible encoding method for 3.5" disk sectors? I expect differences in sector length and file/directory structure, but what about the encoding itself? I guess IBM encoding would have to be compatible since programs are available for the Amiga to format/read (+ write?) IBM 3.5 inch disks. I think one of the C-64 emulators even reads 1581 disks, so it would have to be compatible too. Can someone illuminate me on this question? Marcel A. LeBlanc | University of Toronto -- Toronto, Canada leblanc@eecg.toronto.edu | also: LMS Technologies Ltd, Fredericton, NB, Canada ------------------------------------------------------------------------------- UUCP: uunet!utai!eecg!leblanc BITNET: leblanc@eecg.utoronto (may work) ARPA: leblanc%eecg.toronto.edu@relay.cs.net CDNNET: <...>.toronto.cdn
daveh@cbmvax.UUCP (Dave Haynie) (11/15/88)
in article <8811101847.AA22940@godzilla.eecg.toronto.edu>, leblanc@eecg.toronto.edu (Marcel LeBlanc) says: > Summary: 3.5 inch sector encoding question > > [] > Can somebody tell me if Amigas, IBMs, 1581s (CBM 8-bit), and Ataris > use a compatible encoding method for 3.5" disk sectors? Yes and no. They all use a form of MFM encoding (good to leave out Macs, since they use a GCR format). IBMs and Ataris use pretty much the same 9 sector/track format (720K), nothing really tricky there. 1581s store 10 sectors/track (800K), and Amigas store 11 sectors/track (880K). The IBM/ST format lets the controller write arbitrary sectors; there's enough space left between them to account for head positioning slop. The 1581 always writes full tracks, so sectors are always positioned accurately, and there's no need for slop areas between them. Amigas always read write full track, and in fact leave no space between sectors at all. > I expect differences in sector length and file/directory structure, but > what about the encoding itself? The Amiga actually does the MFM encoding and decoding with the blitter in normal operation; it reads raw MFM in from disk. This allows the Amiga to read or write any MFM format that uses the 1-meg unformatted density encoding, this includes both IBM/ST and 1581, though the arrangement of these formats make lend itself better to CPU driven decoding than blitter driven decoding. While the 1581 uses hardware encoding and decoding, it's capable of reading, but not writing, full raw tracks. So a C128 program could, at least in theory, read an Amiga disk, but it couldn't write one. With IBM type formats, it probably depends on the floppy controller. These all do their encoding and decoding in hardware, and are only guaranteed to read and write individual sectors. Any IBM based system with a floppy controller chip than can read and write full raw tracks could read and write Amiga disks with the appropriate program, but I suspect most controllers can't do this. An IBM controller could probably read a 1581 disk with the right program, but again, without that full track write capability, it can't write the 1581 format accurately. > Can someone illuminate me on this question? There's a candle. If need a flashlight, let me know. > Marcel A. LeBlanc | University of Toronto -- Toronto, Canada -- Dave Haynie "The 32 Bit Guy" Commodore-Amiga "The Crew That Never Rests" {uunet|pyramid|rutgers}!cbmvax!daveh PLINK: D-DAVE H BIX: hazy Amiga -- It's not just a job, it's an obsession
dave@dms3b1.UUCP (Dave Hanna) (11/15/88)
In article <8811101847.AA22940@godzilla.eecg.toronto.edu> leblanc@eecg.toronto.edu (Marcel LeBlanc) writes: > Can somebody tell me if Amigas, IBMs, 1581s (CBM 8-bit), and Ataris >use a compatible encoding method for 3.5" disk sectors? I expect This is from memory, so all details may not be accurate, but the answer is No, they don't. IBM's, and, I think, Atari's, use the industry standard (standard even before IBM started using it) MFM (modified frequency modulation), and use a gap between each sector to allow for speed variances and start/stop recording uncertainty. The controller in the Amiga has the ability to use that format, but the standard Amiga format uses GCR (Group Coded Recording), which is also what the Apple II used (not sure about Mac). They also read and write an entire track at a time, which allows them to eliminate inter- sector gaps, and get more data on a track (11 sectors, vs. 10 maximum if you allow minimal gaps). >Marcel A. LeBlanc | University of Toronto -- Toronto, Canada Hope this helps. Dave Hanna -- Dave Hanna, Daltech MicroSystems | "Do or do not -- There is no try" P.O. Box 584, Bedford, TX 76095 | - Yoda (214) 358-4534 (817) 540-1524 | UUCP: ...!killer!gtmvax!dave |
kodiak@amiga.UUCP (Robert R. Burns) (11/16/88)
In article <160@dms3b1.UUCP> dave@dms3b1.UUCP (Dave Hanna) writes: )... The controller in the Amiga has the ability to use )that [MFM] format, but the standard Amiga format uses GCR )(Group Coded Recording), which is also what the Apple II used... That's backwards. The Amiga was originally spec'd to read/write Apple II 5 1/4" disks (for BASIC program portability), then Paula was revised to read/write IBM PC (MFM) 5 1/4" disks, then we went with 3 1/2" MFM disks and the proprietary sector layout that allows the blitter to be used to advantage to read sectors. - Kodiak -- | / _ _|' _ |/ Bob Burns . . . . .---. . |/ (_)(_)|(_\|\ Ursa Major / \ |\ /| | | __ / \ |\ Kodiak \ _______/ A \| \/ |_|_|___|/ A \ | \ Software "Dedicated to the Science of Fun"\_________
mlelstv@faui44.informatik.uni-erlangen.de (Michael van Elst ) (11/17/88)
In article <5231@cbmvax.UUCP> daveh@cbmvax.UUCP (Dave Haynie) writes: >in article <8811101847.AA22940@godzilla.eecg.toronto.edu>, leblanc@eecg.toronto.edu (Marcel LeBlanc) says: >> Summary: 3.5 inch sector encoding question >> >> [] >> Can somebody tell me if Amigas, IBMs, 1581s (CBM 8-bit), and Ataris >> use a compatible encoding method for 3.5" disk sectors? > >... Any IBM based system with a floppy controller >chip than can read and write full raw tracks could read and write Amiga >disks with the appropriate program, but I suspect most controllers can't >do this. > A friend who uses an CP/M computer has tried to read Amiga disks with his WD1797 controller. We've got results. But there are some problems with the Amiga format. First, the controller cannot write full tracks because some data bytes are interpreted as format control codes to generate CRCs, SYNC bytes, etc. So writing Amiga disks will be impossible. (Say nearly, you could encode your data to ensure that the complete track information does not contain any of these control codes, but its easier to read other formats with the Amiga controller). Second, reading is done well with a read track command. You get the encoded data and have to split the odd/even bits but you can reconstruct the data sectors. EXCEPT for data that is placed at the index hole of the disk !! The controller starts/stops the read track command when an index pulse is detected. Thus you have to mask this signal and feed a timer based signal into the controller chip. Then you get all sectors. If someone is interested. Please E-mail. Michael van Elst E-mail: UUCP: ...uunet!unido!fauern!faui44!mlelstv