Hanging a 2nd disk off a 3b2-310?

[Peter Fales]

In article <982 at vsi.COM>, friedl at vsi.COM (Stephen J. Friedl) writes:
> In article <7259 at chinet.chi.il.us>, randy at chinet.chi.il.us (Randy Suess) writes:
> 
> > Yes, you can get any PC Klone type
> > hard disk [for the 3B2] that is 1024 cylinders - 8 heads or less...
> 
> While there does indeed seem to be a limitation on 1024 cylinders,
> the 3B2 is happy to use up to sixteen heads (indeed, the stock CDC
> drives that ship from AT&T have nine heads).  Congruent Technologies
> appears to have found a way to format a drive with > 1024 cylinders,
> but we've not been able to do so.


Sorry, this is pretty sketchy, but...

The earliest models of the 3B2/300 (possibly 310?) did only support disks
with eight heads or less.  The following simple modification will
allow an early model 3B2/300 to use more than eight heads:

DISCLAIMER:  I have done this myself and seen it work, however, NEITHER
I NOR AT&T CAN TAKE ANY RESPONSIBILITY FOR ANY DAMAGE TO YOUR SYSTEM
AS A RESULT OF ATTEMPTING THIS MODIFICATION.


My notes don't indicate what this chip 
is, but it is right next to the Hard
Disk controller chip in this physical
location.
	|
	|
	v

    --------- 	-------------
    |       |	|	    |
    |     12|-+ |	    | <--- NEC Hard Disk Controller Chip
    |       | | |           |		1) Isolate Pin 23
    |       | | |	    |		2) Add Wire from pin 27 to pin 12
    |       | | |	    |
    |       | | |	    |
    --------- | |	    |
	      | |	    |
	      | |	    |
	      | |	  27|------+
	      | | 	    |      |
	      | |	  23|--X   |
	      | |	    |      |
	      | -------------	   |
	      |			   |
	      +--------------------+

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