Date   : Wed, 11 Jun 2008 14:10:00 +0200
From   : anders.carlsson@... (Anders Carlsson)
Subject: 5.25" Disks for sale

Ian Wolstenholme wrote:

> It's a real shame that 5.25" HD discs don't work on Beebs.

However, wouldn't it be possible to adopt a 5.25" HD drive from a PC to work 
on a BBC Micro, probably with a modified (A)DFS? I don't know why anyone 
would want to do that today though, other than proof of concept.

> Unless somebody knows a trick equivalent to covering up the second hole
> on 3.5" HD discs?

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

5.25" DD (48 tpi) and QD (96 tpi) soft sectored: 300 Oe
5.25" HD: 600-675 Oe (different sources)
3.5" DD: 600 Oe
3.5" HD: 750 Oe
3.5" ED (2.88 MB): 900 Oe

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? A number of systems back in the 1980's used QD 
disks, i.e. the higher capacity Commodore PET disk drives. They store 500K 
per side, and while some DD disks may work at that density, most will fail 
after some time.

Best regards

-- 
Anders Carlsson