Path: utzoo!utgpu!watserv1!watdragon!tiger!mwandel
From: mwandel@tiger.waterloo.edu (Markus Wandel)
Newsgroups: comp.sys.amiga
Subject: Re: HD floppies
Message-ID: <21758@watdragon.waterloo.edu>
Date: 8 Mar 90 23:22:36 GMT
References: <1990Mar5.205252.28816@Neon.Stanford.EDU> <3891@nmtsun.nmt.edu> <9858@portia.Stanford.EDU> <gZxfIWu00Xc1Q0Pl4R@andrew.cmu.edu>
Sender: daemon@watdragon.waterloo.edu
Reply-To: mwandel@tiger.waterloo.edu (Markus Wandel)
Organization: U. of Waterloo, Ontario
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In article <gZxfIWu00Xc1Q0Pl4R@andrew.cmu.edu> md3b+@andrew.cmu.edu (Matthew Donald Drown) writes:
> 
>   I'm not sure about 3.5" disks, but the disks for 5.25" weren't
> any different that I know of.  Before my Amiga I had a venerable
> C64, because I ran a BBS I bought a SFD 1.2meg drive.  The drive
> would only format cheap disks, I bought a ten pack of high density
> 5.25" and the drive gave me format errors.  I do know that the 
> 3.5" disks have some physical difference, but this sounds like a
> marketing ploy, no clue.

Before everybody starts taking this as evidence that there is no such thing
as 5.25" high density disks either, it should be pointed out that the
SFD 1001 drive does in fact store a megabyte on regular double density "360K"
disks.  It uses a double sided, 80 track mechanism (360K drives use 40 track
mechanisms), and it uses a variable bit-rate GCR encoding which packs a little
more than the usual amount on each track.  But it's still a regular "double
density" drive, and it uses regular "360K" disks.  The high-density disks
are a different animal, and the SFD 1001 can't use them for the same reason
that most other double density drives can't.
 
Note: "Single Density" --> obsolete FM encoding scheme.
      "Double Density" --> 250kbps MFM encoding, (i.e. 360K 5.25" disks, the
                           Amiga disks, etc).  Also applied to other schemes
                           (like the GCR encoding used by C64s and Macintoshes)
                           when they give similar recording densities.
      "High Density"   --> 500kbps, 360RPM, 1.2 meg floppies in the PC AT,
                           or 500 kbps, 300RPM, 3.5" 1.44 meg floppies
      "Quad Density"   --> a term sometimes applied to higher-than-normal
                           capacity disk systems, such as 80-track drives in
                           the SFD 1001, various CP/M systems, etc.  Usually
                           used the same disks as the double density drives.

Disclaimer:  I don't really know what I'm talking about, so keep the flame
throwers on "medium rare" please and just correct any errors.

Markus Wandel
mwandel@tiger.waterloo.edu
(519) 884-9547