Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!hellgate.utah.edu!dog.ee.lbl.gov!ucsd!usc!wuarchive!mit-eddie!uw-beaver!cornell!johnhlee From: johnhlee@svax.cs.cornell.edu (Johnny H. Lee) Newsgroups: comp.sys.amiga Subject: Re: Misunderstanding about my q. CrossDos (or something else ...) on a PC ? Message-ID: <45708@cornell.UUCP> Date: 12 Sep 90 16:00:30 GMT References: <49392@olivea.atc.olivetti.com> Sender: nobody@cornell.UUCP Reply-To: johnhlee@cs.cornell.edu (Johnny H. Lee) Organization: Cornell Univ. CS Dept, Ithaca NY Lines: 31 In article lupe@alanya.Germany.Sun.COM (Lupe Christoph - Sun Germany Consulting - Munich) writes: >Can't. Most floppy controllers in this world use MFM coding. Commodore >has used GCR on the 64, and Commodore-Amiga is using it on the Amiga. > >The Amiga floppy hardware is more flexible than the regular integrated >floppy controllers. It can read/write *any* encoding (at least, MFM). >The issue is that the Amiga has support hardware to encode/decode GCR, >but not MFM. But MFM coding/decoding can be done in software, so it's >just slower. Er, just to point something out here, the AmigaDOS disk format v1.0 (not AmigaDOS 1.0) does *not* use GCR. It is MFM, only that the data bits are stored in a stream of the odd bits followed by the even bits (or is it the other way around?) That is, a chunk with the odd bits of the data are stored first followed by with a chunk with the even bits of the data. Although the organization of the bits of the data is not the same as on the PC's (i.e., contiguous 8 bit bytes,) the bit are indeed stored on the disk using MFM encoding. Also, the Amiga does not have GCR encoding support in hardware. GCR encoding must be done by software (as is MFM, FM, RLL or any other encoding scheme.) It is because of the simplicity of the Amiga's disk controller w.r.t. raw disk bits that gives it its flexibility (software reads from and writes to the chip a stream of raw disk bits.) Other than that, I agree with everything Lupe said. ------------------------------------------------------------------------------- Will Ada overload the ship? Next time on AmigaDos: The Next Generation. John Lee Internet: johnhlee@cs.cornell.edu The above opinions of those of the user, and not of this machine.