Odd Q-Bus questions 18/22bit

From: Jerome Fine <jhfine_at_idirect.com>
Date: Tue Aug 18 11:33:15 1998

>Allison J Parent wrote:

> < 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.

Jerome Fine replies:

This is good news indeed. I was worried that the addition
of the extra address lines in an AB/AB or Q22 backplane
could damage the CPU. In the BA23/BA123 boxes
which are the usual backplanes that are available, the
first 3/4 slots are ABCD.

> < 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.

Well, I always thought that RSX and RSTS/E were far
better of with more memory. Also, with V5.0 of
RT-11, the availability of 4 MBytes and a VM: was highly
useful - not needed, but very nice. Of course, until
recently, DEC memory boards were so expensive that
more than 1/4 MByte was not worth while in any case as
opposed to SIMMs with the PC. However, a half MByte
board (M8067) is now so inexpensive that it is no longer
a problem.

> 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).

What hardware did you use to connect the RQDX3 to the RX50/RX33
floppy drives? In general, I found the floppy to be far too slow
and if I was jumping up the an RX33, for the same price (at current
cost for a hard drive) I would prefer at least an RD51.

> 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.

You can always power the disk drives with an auxiliary power
supply from a PC. In that case, you can even have 2 hard
drives and 2 floppies. Otherwise, with just the one hard
drive (under the tube), it is indeed on the edge of the PS
if the VT103 supplies all the power. One other option I
mentioned is that a SIGMA RQD11-B (MFM controller)
uses about the same power as an RQDX3, but has BOOT
ROMS. As a result, you can use just the dual 11/23 and
no BDV11. Then there is enough internal power to run
everything for a reasonable period of time (likely at least
an hour), but if you want a longer period of time or
you are going to use 2 hard drives, then stick the
hard drives on the eternal PC power supply.

> < 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.

YES!! If run for a long time. But for short demos of
an hour or less, the VT103 was highly effective. Most
individuals who were familiar with the VT100 did not
recognize the VT103. So when the demo was given,
the first reaction was to ask about the computer - they
saw only a VT100. We used to say that we had substituted
clever squirrels inside the VT100 instead.

> < 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!

I even heard that someone had re-wired the backplane
to allow a MicroVax II (ABCD slots for the first 2).
Now imagine if DEC had sprung the VT103 on the
PC world as a PC at PC prices with a 150 watt power
supply (and a bigger fan) to easily allow hard drives under
the tube. And later, had gone to the MicroVax II as
a standard option. The 10 year late DEC PCs would
have been initially based on the PDP-11 and could
then have used the VAX. The only thing lacking was
a pricing model to compete with the XT and the AT
(and a will by Ken Olson to sell to the masses).

> < 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.

I understand that a total of 32 solder connections are
required. I once saw the re-wired backplane. It
seemed to have been done with wire-wrap wire
since the solder points were so small.

It does not seem that more than a few others use the
PDP-11 to any extent and even fewer use RT-11.
I guess that perhaps I still quality to be part of the
group who fix hardware since I was involved in the
VT103 conversion. At one stage, there was a
consideration of if it was worthwhile to put an
ESDI hard disk controller into the VT103 and use
an ST8760E 5 1/4" hard drive, naturally with
an external power supply and a fan right beside the
drive. In RT-11, that is 20 partitions. SIGMA
made an RQD11-DESDI dual controller which
could handle 2 of the drives.

Sincerely yours,

Jerome Fine
RT-11/TSX-PLUS User/Addict
Year 2000 Solutions for Legacy RT-11 Applications
(Sources not always required)
Received on Tue Aug 18 1998 - 11:33:15 BST