Date   : Thu, 01 Nov 2007 08:03:25 +0000
From   : pete@... (Pete Turnbull)
Subject: BBC drives

On 01/11/2007 07:16, Mike Tomlinson wrote:

> [[[ As an aside, I always thought a 1.2Mb drive slowed its spindle 
> speed to 300rpm to read/write double-density discs, but was not sure 
> how this was done (whether the drive senses the disk density and 
> chooses the appropriate speed, or whether it is done by the disk 
> controller.)
> 
> A google suggests that the drive doesn't actually slow down, but 
> supplies the data to the controller at a higher rate

That depends on the drive.  On many 5.25" HD drives, the density select 
pin (pin 2) can be linked to control the speed as well, and that was the 
common way of doing things at one time.  Indeed, judging form the number 
of erroneous web pages I've seen over the years, many people seem to 
mistakenly believe that pin 2 is the speed select, rather than the 
density select.

-- 
Pete                                           Peter Turnbull
                                               Network Manager
                                               University of York