Date   : Sun, 03 Apr 2005 09:38:31 +0100
From   : Jon Ripley <jon@...>
Subject: Re: BBC disk drives

W.Scholten wrote:
> Jon Ripley wrote:
>>Any 3.5" drive will do, even the cheap and cheerful HD ones that are are
>>usually destined for PeeCees will work perfectly.
> 
> No. See the archives for a message describing differences in drives.
> None of the 1.4MB drives I tried ever worked.

Yes. They do. I'm not suprised. AFAIK There is no such thing as a 1.4MB 
drive. Any that do exist are aberrations and probably custom drives made 
for very specific purposes, none are commercially available and as such 
I would imagine that they would be prohibitively expensive. However...

I have used several different quad density disk drives without problems 
on a range of BBC computers. There are some links on the keyboard that 
control drive stepping that may need to be altered to ensure better 
compatibility.

Note: A quad density drive is also known as a high density drive, and 
quad density disks are also known as high density disks.

Quad density disks store up to 2Mb of data and not 1.44Mb as is commonly 
believed. All good quad density drives support double density and single 
density modes, if they didn't then modern RISC OS, Mac OS, Linux, Unix, 
Windows, OS/2, Solaris, etc machines would not be able to read or write 
their respective single and double density disk formats and tools such 
as OmniDisk would be useless.

If you do purchase a quad density drive do not tell the shop keeper that 
it is destined for a BBC, it will usually only confuse them and they may 
decide to invalidate any warranty that would have been included 
otherwise. If the drive does not work with the correct media and 
link/CMOS settings then you should return it as faulty. You mileage with 
shop keepers may vary. To be fair though, all (1) shop keepers I know 
who do know what they are talking about have had no problems with 
try-after-you-buy and return-if-not-compatible.

Media compatibility can be an issue, quad density disks are not designed 
to be formatted to double or single density formats. It is possible in 
the majority of cases to fudge the disk density but the resultant life 
expectancy of the disk and its data is variable. To do this you can 
disable the density select switch at the front-left corner of the drive. 
Be aware though that many quad density drives only emulate single 
density and double density modes and there may be issues using the disks 
  on machines with real double or single density drives - personally I 
have not had any problems with this. Low quality quad density disks seem 
to work best and are the most available type.

If you can track down a software density select drive then you should 
have no problems with any media as the drive will automatically use 
whichever density the BBC asks it to regardless of media type. Finding a 
software density select drive is highly-unlikely to impossible as no 
self-respecting PC dealer will have the faintest idea what one is.

There is some more info here:
http://homepage.ntlworld.com/rpsprowson/bbc/reference.htm#35indisc
http://mdfs.net/Docs/Comp/Disk/Densities

As a side note, the maximum capacity of a floppy disk is about 4.5Mb 
when using a variable rotation speed octal density drive.

Have fun,
Jon Ripley
-- 
http://jonripley.com/