Date   : Tue, 18 Jul 2006 13:26:43 +0100 (WET-DST)
From   : Peter Coghlan <PCOGHLAN@...>
Subject: Re: What types of

>
>I'm looking for a 3.5" floppy drive for my Beeb and was wondering if anybody
>has had any success in getting a PC 1.44Mb drive to work ? Can't believe the
>prices that I'm seeing on Ebay for original drives !
>
>Failing that, would an old DSDD 3.5" drive from say an Atari or Amiga
>external unit work ?
>
>Happy to take a soldering iron to a floppy to make it work if necessary :-)

There is a fair bit of misinformation around regarding this topic.
Lets see if I can add some :-)

The easiest 3.5" PC drive to get working on a BBC is probably an old DSDD one.
It is by no means impossible to get a newer 1.44MB HD drive to work but there
are a number of gotyas.

Firstly, you can't use the drive in HD mode and you must use it in DD or SD
mode. From the drives point of view, DD and SD are the same thing.

Most drives will look for the extra hole in the disk in order to tell if a
disk is HD rather than DD and act accordingly. Using HD disks with or without
the hole covered up may cause problems of one kind and another. Things may
appear to work but long term reliability can be impaired.

Secondly, lots of newer drives have a "feature" which allows them to step
to different tracks faster which causes problems on BBCs with 8271
controllers, if not others. On hard drives, this is called "buffered seek".
I presume it is called the same thing on floppy drives. Traditionally, it
was necessary to wait a fixed period of time between sending track step
pulses to the drive. On floppys with this new feature, you can send lots
of track step pulses very quickly and the drive will signal when it has
reached the required track. This signalling is done by suppressing the
index pulses until the required track is reached. A BBC with 8271 controller
does not like this and frequently responds with "Drive error 10"
(drive not ready). I am not sure but I think Masters are more forgiving.
This feature will need to be disabled or worked around if it is found to be
present and causing problems.

Thirdly, most PC floppy drives come jumpered as drive 1 with cable twists
being used to implement drive 0. The twist in a PC floppy cable is not
suitable for using with a BBC as it swaps more signals than it should
for this purpose. If you are using a PC floppy cable, do not use the
socket(s) after the twist. If you want your drive to be drive 0,
change the jumpers instead.

There are similar problems and more using 1.2MB HD 5.25" drives on a BBC.

Regards,
Peter.