QBus chassis and backplanes

From: Jerome H. Fine <jhfinexgs2_at_compsys.to>
Date: Sun Sep 19 20:16:52 2004

>Pete Turnbull wrote:

> In view of the recent discussion about which backplane(s) go with which
> CPU(s) and some similar discussion on alt.sys.pdp11, I've collected
> together some of my data on backplanes and chassis. They're in a text
> file at
> http://www.dunnington.u-net.com/public/PDP-11/QBus_chassis
> If anyone wishes to add to that, feel free to send me information :-)

Jerome Fine replies:

I am not sure just where to add the information about a VT103. I suspect
that the backplane in use is the 2 * 4 (H9281-AB) or a 4 * 4 (H9270).
Along with a few other bits of hardware, including a fan and a better
power supply, a VT103 is almost identical to the VT100 upon which
the VT103 is based. And since the location in a VT103 where the
backplane is located is empty in a VT100, it is possible to say that
a VT103 is the same physical size as a VT100. It is even possible
to place a hard disk drive under the tube (there is sufficient room for
a full height 5 1/4" hard disk drive, let alone a SCSI 3 1/2" hard
disk drive), but placing a hard disk drive there is certainly not
a DEC solution.

Back in the 1980s, DSD (Data System Design) sold many VT103
systems with a DSD 880/30 combination which emulated 3 * RL02
disk drive and single RX02 floppy drive. The controller interface
was a single dual Qbus board which contained boot ROMs as well.
Normally an M8186-AA (dual 11/23) was used, but an M8192-AA
(dual 11/73) was also possible. Since the original backplane was
only 18 bits, only 256 KBytes could be used. But after the backplane
was enhanced to be 22 bits, up to a full 4 MBytes could be used,
although the DSD 880/30 controller interface could only handle
18 bit addresses up to 256 KBytes. Under RT-11, it is possible
to add a bounce buffer for both the DLX.SYS and DYX.SYS
device drivers, although I am aware of it being done ONLY for
the DYX.SYS device driver.

Sincerely yours,

Jerome Fine
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Received on Sun Sep 19 2004 - 20:16:52 BST

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