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From: grr@cbmvax.UUCP (George Robbins)
Newsgroups: comp.sys.amiga
Subject: Re: An Amusing Anectode (The tale of the 2 Meg disk)
Message-ID: <2119@cbmvax.UUCP>
Date: Wed, 15-Jul-87 07:29:56 EDT
Article-I.D.: cbmvax.2119
Posted: Wed Jul 15 07:29:56 1987
Date-Received: Fri, 17-Jul-87 06:13:53 EDT
References: <398@rocky.STANFORD.EDU> <1649@cadovax.UUCP> <873@omepd>
Reply-To: grr@cbmvax.UUCP (George Robbins)
Distribution: world
Organization: Commodore Technology, West Chester, PA
Lines: 43

In article <873@omepd> hah@isum.UUCP (Hans Hansen) writes:
> In article <1649@cadovax.UUCP> keithd@cadovax.UUCP (Keith Doyle) writes:
> >In article <398@rocky.STANFORD.EDU> ali@rocky.stanford.edu (Ali Ozer) writes:
> >>Anyway, now I have a 2.0 Meg capacity floppy disk. 8-)
> >
> >Well, if 2.0M 3.5" floppys achieve their high density in the same way
> >HD 5.25" floppys do, you might not want to use it.  HD disk drives use
> >a higher write current, because the floppy media is less sensitive, which
> >for some reason permits higher density.  Normal disk drives will not
> >put out a high enough write current to write the media reliably.  I
> >remember having all kinds of problems trying to format HD disks on
> >non-HD drives until this was explained to me, and I gave up trying.
> >
> The new HI-Density Disks use PERPENDICULAR rather than PARALLEL magnetic
> particle alignment.  The 2Meg floppy doubles the track count or has 160
> cylendars.  Upgrading the A1000 with a 2Meg drive while sounding neet
> and deliver more bytes for the buck, unless commodore gets on the band
> wagon (HINT HINT), will cause a compatibility nightmare.  What I would
> like to see is a driver that can recognise both types of drives and
> automatically adjust the cylendar count.
> 
> Hans

Oh, confusion! 8-(  The new 1.44 MB drives used on the IBM PS/2 machines
don't use perpendicular recording, this is still pretty much off in the
future.  They don't have more tracks, rather they do use the 500KB/s data
rate like the 8" floppies and AT 1.2 MB drives to increase the bit density
on a track and get more sectors/track.  They do require special hi-density
diskettes, which have a higher magnetic coercivty, meaning they need a
stronger magnetic field for writing/erasure, but can, in effect, support
writing "smaller" bits on the disk.

In any case, the floppy controller section of the Amiga chipset does not
currently support a 500KB/s data rate in MFM mode, making the issue kind
of academic at this point.  You might be able to accomplish something in
the "Apple GCR" mode, but as I understand it, there is considerably more
software bit manipulation in the read/write process that would probably
make this less attractive.

-- 
George Robbins - now working for,	uucp: {ihnp4|seismo|rutgers}!cbmvax!grr
but no way officially representing	arpa: cbmvax!grr@seismo.css.GOV
Commodore, Engineering Department	fone: 215-431-9255 (only by moonlite)