David Gahris <dgahris@eece.maine.edu> provided the following information:

> Are you sure about the hardware differences?  

Yes.  

* I have looked inside my 128DCR and inside stand-alone 1571s.  

* There is no 6526 or 8521 in the drive section of the 128DCR.  I believe the 
  5710 handles fast serial because the 5710 is a Commodore custom chip and 
  128 fast serial is a Commodore custom protocol.  [Ed's note: Commodore lists
  NTE229, ECG229, SK3246A/229, and 121-Z9021 as substitutes of the 5710.]

* There is no 177x or heat-shrink-wrapped daughterboard in the drive section 
  of the 128DCR.  I believe the Motorola plastic quad flat-pack chip handles 
  MFM because I am pretty sure that I have seen this chip in IBM PC drive 
  mechanisms.  

* The 1571cr ROM works great in 1541 mode but not at all in 1571 mode in a 
  standalone 1571.  

* Olaf Seibert informed me that the 1571cr ROM contains a string to the 
  effect of "5710 (c) 1986 by c. hauck"