Date   : Fri, 26 Oct 1990 07:43:22 PDT
From   : Sprague.Wbst311@xerox.com
Subject: Xerox 820-II cards

Grumble!  This bounced the first time.  It's a little late, but still applies.


In reference to the card in Steve's Xerox 820-II, and in the spirit of general
information sharing (I saw some incorrect info), I have written the following
note.  :-)


As has been pointed out, the Xerox 820 has NO card edge slots.  The 820-II,
16/8's or what have you ... the CPU board is the same for all of them, had two
card edge slots near the left side.

There were only 4 cards for Xerox 820's made in the USA.  Two of them were for
the left card connector and two of them were for the right.  In all cases, when
I say right and left, it will be as if I was looking into the machine from the
rear.

The left slot is for the drive controller.  It will contain either a floppy
controller card (works with both 5.25" or 8" drives), a hard drive interface
card (8" drives only), or NO board if it's a 16/8 machine with a DEM (Disk
Expansion Module).  Off the top of my head, the hard drive card is maybe 3"
tall, while the floppy controller is maybe 4" tall.  NEVER connect the floppy
controller card to a hard drive, as you will blow the floppy/hard drive
controller board down the line.  I do not think connecting a hard drive
interface board with floppy's will cause any damage, but I wouldn't chance it.

The right slot will contain NO board if it's a standard Xerox 820-II, a 16/8
board if it's a 16/8 (that's an 8086 system on a card, for those of you who do
not know), or a DEM buffer board if this is a 16/8 with DEM.

Now that I think of it, there was also a 256K memory expansion board for the
16/8, which plugged directly into the 16/8 board.  Very hard to find and
expensive.

I have seen notes where Rank Xerox (in England) may have made some additional
cards which went into the DEM.  (Note:  The DEM has a card cage which can hold
4 or 5 cards, one of which would be the 16/8 card.)  There may have been an RX
memory expansion card (256K) for the 16/8, and there may have been an RX fancy
video graphics board.

The most notable incorrect things I saw was that sombody said the 16/8 board
contained an 8088, and that the DEM connected up to the 16/8 board.

                       ~ Mike  (Sprague.Wbst311@Xerox.Com)