[BBC-Micro] Technomatic hard disk units

[Jonathan Graham Harston]

>Message-ID: <1EEB761125F54CE283B8977B473AFB16.MAI at ukhosting.ltd.uk>
 
"Ian Wolstenholme" <BBCMailingList at beebmaster.co.uk> wrote:
> I was always led to believe that using MFM drives with
> an RLL controller was a "bad" thing because you were
> squeezing more sectors per track onto the drive than
 
MFM and RLL are different ways of encoding the bits on the track
surface, like the difference between FM and MFM. There are exactly
the same number of bits on the disk surface, the disk itself has
no knowledge of what you have done to it.
 
In fact, MFM is RLL, it's RLL1:3. The digits indicates the minimum and
maximum number of data bits that can go past before a clock pulse is
needed.
 
> I'm sure it's down to a question of reliability, and I've
 
You are depending on the accuracy of the data seperation and
clocking circuitry. The larger the RLL factor the longer the data
seperator may have to go before a real clock pulse comes along to
ensure everything is synchronised.
 
http://www.pcguide.com/ref/hdd/geom/dataRLL-c.html is a very good
explanation.
 
-- 
J.G.Harston - jgh at arcade.demon.co.uk - mdfs.net/User/JGH
BBC BASIC for the Sinclair Spectrum - http://mdfs.net/Software/Spectrum