Subject: Re: Apple II-Or Come on people, It's a 20 year old computer
Newsgroups: comp.sys.apple2
References: <394F0452.D41@tirix.org> 
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From: david@uow.edu.au (David Wilson)
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Date: 9 Aug 2000 09:23:46 +1000
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pausch@saafNOSPAM.se (Paul Schlyter) writes:
>I have a similar observation: 5.25" MFM floppies on a PC work faster
>than 3.5" MFM floppies on the same PC.  OK, the 5.25" floppy contains
>"only" 1.2M, compared to 1.44M for the 3.5" floppy, but the
>difference in reading speed appeared much greater than that.  This
>became quite obvious when I, a few months ago, backed up all my old
>5.25" PC floppies on CD.

It may also have something to do with 1.2Mbyte 5.25" drives running at
360rpm (just like an 8" floppy) instead of the 300rpm used by DD 5.25"
and DD/HD 3.5" drives.

Here are the PC 5.25" formats:

disk    speed           data rate       trk     sector  trk/hd
size    rpm     s/rev   kb/s    scheme  kb      cnt*sz  count   KB
--------------------------------------------------------------------------------
5.25"   300     0.200   250     MFM     50.00   8*512   40/1    160     SSDD (3)
5.25"   300     0.200   250     MFM     50.00   9*512   40/1    180     SSDD (3)
5.25"   300     0.200   250     MFM     50.00   8*512   40/2    320     DSDD (3)
5.25"   300     0.200   250     MFM     50.00   9*512   40/2    360     DSDD (3)
5.25"   300     0.200   250     MFM     50.00   9*512   80/2    720     DSDD

5.25"   360     0.167   300     MFM     50.00   9*512   40/2    360     DSDD (4)
5.25"   360     0.167   300     MFM     50.00   9*512   80/2    720     DSDD

5.25"   360     0.167   500     MFM     83.33   15*512  80/2    1200    DSHD (4)

(3)	IBM PC
(4)	IBM PC/AT

Note that some 1.2Mbyte drives read DD disks at 360rpm (and 300kb/s) while
others slow down the motor to 300rpm (and 250kb/s). 1.44Mbyte also run at
500kb/s but at 300rpm and this is how they squeeze more data on a track than
a 1.2Mbyte drive.
--
David Wilson  School of IT & CS, Uni of Wollongong, Australia