Substituting DSHD for DSDD disks (or DS2D if you prefer)

Chuck Guzis cclist at
Wed Jan 27 10:49:33 CST 2016

On 01/26/2016 09:07 PM, Eric Smith wrote:
> On Tue, Jan 26, 2016 at 7:04 PM, Chuck Guzis <cclist at>
> wrote:
>> You've lost me there.  Both HP and Intel were true MMFM;
> There's more to it than the basic channel code.
> IBM 3740 and Ohio Scientific 8-inch both use "true FM" for the
> channel code, but they aren't compatible.
> The HP 9895 M2FM and Intel M2FM may be the same channel code, but
> the address marks are different, etc.

That's exactly what I was asking.  But you implied that the RX02 was 
MMFM, which, in my experience is not the case.

MFM is a (1,3) RLL code; MMFM is a (1,4) code.  AFAIK, RX02 is a 
combination of (0,1) for headers and (1,3) for data.  WHat the decoded 
clock and data bits actually mean is a separate issue.


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