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Path: utzoo!watmath!clyde!burl!ulysses!allegra!oliveb!hplabs!sdcrdcf!darrelj
From: darrelj@sdcrdcf.UUCP (Darrel VanBuer)
Newsgroups: net.micro.pc,net.micro.apple
Subject: Re: Re: Want to read Apple II disk on IBM PC
Message-ID: <2284@sdcrdcf.UUCP>
Date: Sun, 25-Aug-85 18:37:57 EDT
Article-I.D.: sdcrdcf.2284
Posted: Sun Aug 25 18:37:57 1985
Date-Received: Wed, 28-Aug-85 20:50:36 EDT
References: <125@well.UUCP> <576@mmintl.UUCP> <41@intelca.UUCP>
Reply-To: darrelj@sdcrdcf.UUCP (Darrel VanBuer)
Organization: System Development Corp. R+D, Santa Monica
Lines: 17
Xref: watmath net.micro.pc:5123 net.micro.apple:2104
Summary: 

Can't be done with standard disk controllers.  If you look closely at the
timing and data patterns used by the Apple hardware/software combination,
you find they are using a 1.5 density GCR scheme.  All controller chips
implement only single density FM and double density MFM (or a few other
variants of MFM).  On the other hand, the Apple controller uses less than a
dozen MSI chips and 256 bytes of 6502 code to operate! so it's a relatively
easy controller to emulate (which a few vendors have, as pointed out in
other articles).
-- 
Darrel J. Van Buer, PhD
System Development Corp.
2500 Colorado Ave
Santa Monica, CA 90406
(213)820-4111 x5449
...{allegra,burdvax,cbosgd,hplabs,ihnp4,orstcs,sdcsvax,ucla-cs,akgua}
                                                            !sdcrdcf!darrelj
VANBUER@USC-ECL.ARPA