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Path: utzoo!watmath!clyde!rutgers!cbmvax!daveh
From: daveh@cbmvax.UUCP
Newsgroups: comp.sys.amiga
Subject: Re: Re: MFM format and possible improvments
Message-ID: <1393@cbmvax.cbmvax.cbm.UUCP>
Date: Wed, 11-Feb-87 13:28:28 EST
Article-I.D.: cbmvax.1393
Posted: Wed Feb 11 13:28:28 1987
Date-Received: Thu, 12-Feb-87 18:39:28 EST
References: <4410003@hpcvcd.HP>
Organization: Commodore Technology, West Chester, PA
Lines: 41

> While reading the Hardware Reference Manual, I got the impression
> that the decoding of the floppy bits to real bits is done in
> software.  I hope that is not true.  Perhaps that is part of the
> explanation for why the A1000 is so infernally slow.  With several
> floppy controller chips on the market, this seems counterproductive.

> 	Charles Brown

(A) That is quasi-true.  The decoding is done by one pass of the blitter,
    the encoding done by 3 passes.  All set up by software.  

(B) This has nothing to do with any precieved floppy slowness.  If by
    slowness, you mean that directories take a long time to list out,
    that's based on the DOS file structure (a few levels of software above
    what we're talking about here) and probably the fact that you use
    the DIR command, which holds and sorts all the files it finds.  If
    you're referring to the 256K of Kickstart code that the machine loads
    in less than 30 seconds (a decent test of raw floppy speed), I'm
    not sure what you're driving at.

No commercial floppy chip would be as flexiable as the currently implemented
system.  First of all, the raw data is read from the floppy via an 
interleaved DMA a track at a time.  So once a read/write request is set
up, the data gets transferred to memory directly, as fast as it can come
from the floppy, without any processor intervention and without slowing the
processor down at all.  Once the raw data is in, the conversion is done
by the blitter.  This is a tremendously powerful mechanism, and the basis
for most of the discussion that's going on around here.  We are talking 
about the possiblity of a simple software change that would allow 12 or
13 logical sectors per track, instead of 11.  You also probably know that
the Amiga can easily read IBM or Atari ST formatted disks; just try to
go the other way (hint: The Amiga disk format doesn't really use sectors,
only tracks).  
-- 
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Dave Haynie	{caip,ihnp4,allegra,seismo}!cbmvax!daveh

     "You can keep my things, they've come to take me home"
						-Peter Gabriel

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