27 Nov
2008
27 Nov
'08
1:13 p.m.
On 27 Nov 2008 at 12:41, Fred Cisin wrote:
While you are at it, you should also point out that it
is far from correct
to refer to the interface of the older drive as "MFM", since that is the
encoding, NOT the cabling/interface. An IDE or SCSI drive could certainly
be using MFM or RLL (MFM can also be argued to be one implementation of
RLL).
Okay, call it "the ST-412 interface", but everyone here knows what's
being discussed.
Exactly what "MFM" or "RLL" means, however, is more of a problem.
Manufacturers of controllers varied wildly in their implementation of
the encodings, address marks and checksum polynomials. But yeah, MFM
is (1,3) RLL and what we usually refer to as "RLL" is (2,7) RLL, but
there were ARLL controllers using longer runs (3,11)? to get more
capacity.
I have a question for the guys with the sharp pencils. What is the
minimum satisfactory sampling rate if one wanted to emulate an ST-412
interface and have it RLL (2,7)-capable? Would 16x oversampling of
the 5MHz interface be adequate? How about 8x?
Cheers,
Chuck