VT103 (was Re: Reviving DEC RX01 power supply)

Jerome H. Fine jhfinedp3k at compsys.to
Sun Sep 9 13:01:25 CDT 2007

 >Ethan Dicks wrote:

>>At one even shorter period of time, the VT103 backplane had a
>>PDP-11/73 quad CPU, 4 MB of memory, DHV11 and a Sigma RQD11-EC
>>controller that supported FOUR * 600 MB ESDI Hitachi hard drives
>>although it was essential that all of the hard drives were placed
>>OUTSIDE the VT103 since each required its own fan and all of the
>>hard drives and their fans also used a separate external power
>Wow... that's a lotta stuff for a VT103.
Jerome Fine replies:

The "lotta stuff" was there only for a very short demonstration to
show it could be done.  At the time, the "lotta" stuff" was worth
far more in a BA123 with triple the number of boards, although
those same Hitachi hard drives were used there as well.

>I have a VT103 up in the attic.  I _might_ be able to squeeze a VT100
>case somewhere in my office... these days, though, I'd go with a 3.5"
>SCSI drive and a Qbus SCSI controller.  The real question is, what to
>choose for CPU and memory.  I could easily pull a KDF11B from the
>shelf, add a meg or two on a quad-height board, and between those
>three boards, have a running system.  What I think I'd prefer, though,
>is something with a KDJ11.
>So presuming one is starting from the assumption that you have a VT103
>and a Qbus SCSI controller, what are good choices for the remainder of
>the system?  One can assume that 1MB is minimum, but 4MB wouldn't be
>unwarranted.  I kinda fell off the PDP-11 cart in the KDJ11 era, so
>I'm not as conversant with what's out there, but ISTR that there's the
>dual-height KDJ11A, and there must be a quad-height KDJ11 of some
>flavor, with a variety of common accessories, but I couldn't quote
>chapter and verse.
>I have an 11/53-level KDJ11 board from a DEC comms controller, with
>-11 ROMs installed, but it still has S-box handles, and only has,
>IIRC, 1MB on it.  I'm thinking that any sort of 11/83 or 11/93 board
>is probably going to be priced out of my range, but I'm willing to
>entertain the idea.  I really don't _need_ the speed of an 11/83 or
>11/93, but 4MB on board is attractive (if I've got my boards right).
>Anyone else have any ideas on how to trick out a VT103?
Probably the first step is to add 22 bit address support
to the backplane.  That requires a steady hand with a
soldering iron and probably is best done with old lead
solder since the added wires will be attached to solder
points that already have lead solder.  In any case, almost
no additional solder is needed.  About the best wire to use
is wire-wrap since it is thin, but very sturdy.  Keep all
the insulation except for the 6 mid points where the
wire must be soldered to the existing backplane.  4 wires
with 8 connections each are all that is required.  If you
require help locating the solder points, I can look at one
of the VT103 backplanes that have been modified.  Fortunately,
DEC never attempted to use a PDP-11/03, so the 4 address
lines at not attached to anything else - like power.

And having mentioned power, it is possible to solder
wires to the backplane 5V and 12V that can then be used
to power a hard disk drive.  Any 3.5" SCSI hard drive
can be supported, but the less power needed the better.
The VT103 power supply has a maximum draw on the 5V of
just 16 Amps, so be careful.  Back when all of that work
was first being done, an ST412 (actually an old RD51)
5 1/4" hard disk drive was available and could be just
barely squeezed under the tube.  However, an RQDX1,2
was out of the question since they require 6 Amps for
the 5V.  An RQDX3 is probably OK when used with a quad
CPU like the M8189 or the M8190 (since there are no
boot ROMs on any RQDXn controller).  I guess that you
could type in a boot program (if you don't do it too often)
using hardware ODT - it takes about 5 minutes.

Either a dual or a quad KDJ11 can be used.  Almost EVERY
quad KDJ11 is really the same as a PDP-11/83 except for
the 18 MHz crystal.  And since you can't use PMI memory
without further modification of the first 2 slots to add
ABCD like the first 3 slots on a BA23, it seems that you
are stuck with an ordinary PDP-11/73.

Most VT103 systems came with a paddle card that was intended
to be used with a DLV11-J and a dual PDP-11 Qbus card.  The
paddle card connected the terminal and keyboard to the 4th
channel on the DLV11-J that was then strapped as consol
and the normal 25 pin serial connector on the back could
then be connected to a second serial channel on the DLV11-J
(and probably sent to a serial line printer).

As for the SCSI host adapter, if it has boot ROMs (most
third party DEC MSCP SCSI host adapters do), then you
can easily use a dual M8192 with a DLV11-J as the serial
interface.  Add memory and you are in business - after you
load the SCSI hard drive with files.  In most cases,
an RX23 (3 1/2" HD floppy) can be attached to the SCSI
host adapter which can then be used to transfer small
file.  In addition, if you can find an Iomega SCSI
insider, they support 100 MB replaceable media.

Since both replaceable media drives can also
be attached to a PC running E11, that can serve as your
source for files.  Of course, E11 will also allow your
SCSI hard drives, but Windows is extremely difficult
to convince (I have done it - ask if you want the details)
that there is a SCSI hard drive that has an RT-11 file
structure.  And finally, ask Zane about what you need
to connect a CDROM drive to your SCSI host adapter on
the PDP-11.  On the PC side, I think that E11 will
recognize a DVD drive with a CD and it is possible to
burn a CD on the PC with an RT-11 file structure,
although I will have to recall the details of how the
actual burn was done from the file of the CD image.

Can I answer any other questions?

Sincerely yours,

Jerome Fine
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