Odd Q-Bus questions 18/22bit

From: Allison J Parent <allisonp_at_world.std.com>
Date: Tue Aug 18 08:14:49 1998

< As far as I know, all DEC versions of the VT103 came
< with an 18 bit backplane for the QBus. If an LSI-11/03

Correct.

< is used, I understand it may be ill advised to make any
< changes in the backplane, as well as fruitless, since this
< CPU can use only a maximum of 56 KBytes of memory
< in any case.

Also correct.

< for the PDP-11. However, I have also heard that the
< use of a quad CPU with a 22 bit backplane may also
< risk damage to the CPU in the VT103 environment.

I've done it. The bigest things is the power supply
is somewhat limited.

< BUT, I have seen both the dual 11/23 (M8186) and
< the dual 11/73 (M8192) used with an upgraded 22
< bit backplane within the VT103 along with a full
< 4 MBytes of memory. In addition, there was a

Very doable. The biggest thing is for most DEC OSs
256k (18bit) is plenty.

A good package is a 11/23, 256kram, DLV11j, RQDX3, BDV11.
That gives you 4 serial ports, full memory without backplane mods,
RX50/RX33 floppy and MSCP hard disk (RDxx) and the BDV terminates
the bus plus supplies some of the desireable boots (no mscp).

using a 11/23b or 11/73 you can remove the BDV11 and they have
mscp boots. however the PS is right on the edge.

< tube. The disk drive happened to be a Micropolis
< 1325 of 70 MBytes. And while I would strongly
< recommend against running with a DHV11 for any
< extended period of time due to the lack of a proper

That would overstress the PS and seriously need a bigger fan.

< with the 11/23, and shortly thereafter with the 11/73,
< a far better PC than the MS-DOS/Intel combination
< could produce until the 486 was released in 1989.

you bet!

< If anyone has a VT103 and needs some help with
< how to set it up as well to convert to a 22 bit backplane,
< likely both Megan Gentry and I are able to supply the
< necessary technical information.

I've built a few and have data as well.


Allison
Received on Tue Aug 18 1998 - 08:14:49 BST