On Sun, 18 Mar 2012, Chuck Guzis wrote:
  The problem with the 765 core and 128 byte MFM is
that the whole
 sector doesn't get transferred--only the first 80 (decimal) bytes. 
 I can't help speculating whether that could be something as ridiculously
 improbably simple as an engineer using too high-level a tool, and leaving
 off the 'h' in "80h" 
Which was the cause of a bug in the RS232 driver of the original IBM 5150
BIOS... However, I as going to be more charitable in the case of the FDC
chip and wonder if it was duw to the fact that IIRC the origianl IBM 3740
format used a sector as the equivalent of a punched card, so only the
first 80 chracters were used.
-tony