1.2M HD / 300kbps / single-density

[Chuck Guzis]

On 19 Mar 2007 at 5:35, Dave Dunfield wrote:

> Thanks for the response. So you have not seen this before (single-
> density working at 250kbps but not 300kbps)?

No, but it's not a practice I've followed much.  Many, if not most, 
of the FM-encoded 5.25" (exclusive of the 100 tpi format) formats use 
48 tpi diskettes, so we've always recommended a 48 tpi drive to do 
the work.    And I don't think we have a single system here with your 
SMC controller, although I think I still may have the datasheet 
somewhere here.

It might have happened to us at some point with a customer, but we'd 
have assumed that his was one of the many controllers that don't 
handle FM at all, so our advice would have been the same--find 
another mahine to try.  The problem may have been masked entirely by 
this.

When doing your testing, remember to separate the non-FM capable 
controllers from the FM-capable-but-not-at 300K ones.  Don Maslin and 
I did start doing a fairly exhaustive survey of LSI single-function 
diskette controllers to see what could handle FM and 128-byte 
sectored MFM, but that was long ago, and we didn't include the very 
new multi-I/O chips.  

Maybe it's time for a new census, although I wonder--many systems 
made since about 1995 won't support more than a single floppy anyway--
and I suspect that floppyless desktop PCs aren't that far off from 
becoming the rule (many are still shipped with a 34-pin header on the 
mobo just in case, but that won't stay around, I suspect).

Cheers,
Chuck