Date   : Wed, 11 Jun 2008 21:23:20 +0100
From   : pete@... (Pete Turnbull)
Subject: 5.25" Disks for sale

On 11/06/2008 13:10, Anders Carlsson wrote:

> The coercivity between 3.5" DD and HD disks are closer than it is for 5.25" 
> disks:

I was going to write that, but you beat me to it :-)

> By the way, if I understand correctly the preferred media for BBC computers 
> fitted with a 80 track 5.25" drive would be those QD floppy disks, or maybe 
> most DD work just as well?

Yes, but DD should work just as well.  The density along the tracks is 
exactly the same because the recording method is exactly the same -- QD 
is just a (rather inaccurate) marketing term used by a minority of disk 
manufacturers.  If you do the maths, you'll find the bit density along 
the tracks (about 4000 bits/inch if my mental arithmetic isn't broken) 
is orders of magnitude greater than the density radially from innermost 
to outermost track (48 or 96 bits per inch), so if the media is fine 
enough for 40-track DD it will be fine for 80-track DD.  The only time a 
disk would pass for 40-track use (48 tpi) but not 80-track (96 tpi) 
would be if there was a very small defect, enough to cover less than 
half a track width at 48 tpi (and therefore pass) but still cover a 
substantial fraction of a track at 96 tpi (and therefore fail on that 
track).

-- 
Pete                                           Peter Turnbull
                                               Network Manager
                                               University of York