Date   : Thu, 12 Apr 1990 03:54:21 GMT
From   : zaphod.mps.ohio-state.edu!uakari.primate.wisc.edu!xanth!rlb@tut.cis.ohio-state.edu (Robert L. Bailey)
Subject: 3.5" on 8" Controller?

In article <9004110707.AA07305@ucbvax.Berkeley.EDU> CUMMINGS@S55.Prime.COM
(Kevin J. Cummings) writes:
>A long time ago (years) California Digital (a clearing house for dis-continued
>products and bargins) sold a 5.25" disk drive that they claimed was an 8"
>drive electrically.  I assumed that this means that it had the same electrical
>interface (did that mean the same edge card connector wired the same way) as
>an 8" drive did.  I remember that the 8" drives used a 50 pin daisy chained
>cable, while the 5.25" drives used a 34 pin cable (basically the same signals,
>a few were different, in different places on the cable.  I'm running 720K
>3.5" drives on the same cable as my 40 and 80 track 5.25' drives (using the
>same disk controller).  I have nothing on my 8" controller (never bought
>any 8" drives B^).  I always wondered if I could add a HD 5.25 1.2MB drive
>on the 8" controller?  My 1.2MB drive on my IBM-compatible PC is hooked to
>the same 34 pin connector as my 720K 3.5" drive.  That sorta says no.  Anyone
>successfully run a 1.2MB drive on an 8" controller?

I would think that it should be possible to do just that.  Years ago, I
was putting together a Xerox 820-I and I installed both an 8" SSSD and
3 5 1/4" drives all daisy chained off the same cable.  The trick that I
used was this:  I too, noted that the 50 pin 8" connector and the 34 pin
5 1/4" connector carried the same signals on the same sides, but, they were
located at different pin numbers.  My solution was to use a 34 pin connector
but I used a small saw to cut the connectors slot so that there were no 
longer any stops on the ends of the connector.  (The "stops" as I refer
to them are the ends that keep the connector contact #1 aligned with
the board contact #1)  By removing these, I could then position the
34 pin connector (by offseting it from pin #1) so that the proper signals
were connected to the proper pins of the 8" drive connector.  

I don't have the info handy, but I beleive that I also, had to put a 
jumper wire on the 8" drive so that the motor on line was activated at
the same time as the drive select line.  Other than that, I don't
beleive that I had to do anything special to make things work.

Your problem is the reverse of mine, but, I don't see any reason why
it couldn't be done as long as you get the signals to the right pins!

Bob Bailey (rlb@cs.odu.edu)