New finds: DEC/DSD/MDB

From: Jerome Fine <jhfine_at_idirect.com>
Date: Sat Aug 5 21:16:12 2000

>Kevin Schoedel wrote:

> Jerome Fine wrote:
> >If the 11/23 is a dual board, you may have a bit of a problem in the BA23
> >since the BLUE box was designed with boot boards that might not be
> >compatible with the BA23.
> Because the BA23 has termination, or because it's a 22-bit backplane, or
> something else? The bootstrap is an M8012-YA (BDV11)
> terminator/bootstrap, and neither it nor the other option cards (M8044-HD
> 64Kb, DSD floppy controller, M8043 async) connect the pins for bits 18-21
> (BC1-BF1). The CPU is a dual-width card, and has no apparent revision
> marked, so I guess I should assume it is the 18-bit version.

Jerome Fine replies:

Probably both - because the BA23 already has termination, I do not know if
the M8012 will function correctly in a BA23 box. And an 8" floppy from
DSD is not a speed demon - well no 8" floppy is a speed demon.

Actually, unless you are a PDP-11 hardware hobby person, an 11/23 is not
a great CPU to have fun with. And with just a floppy and 64 KBytes, I would
rather run PDP-11 software under an emulator on a PC. Mind you, I have
a number of M8044 boards to trade if you have something.

> All else being equal (i.e. provided it works) I'd prefer to keep the
> system in its original enclosure anyway, that is, more or less close to
> its previous working configuration.

Everyone to their own taste. I am a software junkie, so I do not really
appreciate this hardware configuration - rare though it may be.

> >> As I found it, the arrangement of cards has gaps, unless the backplane is
> >> *really* weird. The backplane itself is MDB model MLSI 40328 -- anyone
> >> know the layout?
> >If I remember, Transduction used a hex back plane modified to be a Qbus
> >interface with a serpentine use of the "extra" slots. But I can't remember
> >the order.
> For the archives, this backplane is 4x8 and turns out to have the 'usual'
> serpentine configuration throughout; i.e. the same arrangement as slots
> 5-12 in a BA123. It is 18 bit; pins BC1 - BF1 are not connected.

The backplane I am familiar with is a 6 * 9 slot monster. I think that the
first 3 slots might be ABCDAB and the other 6 are ABABAB, but I really
have no clue at all. Whether it was 18 or 22 bit is also something I forget.

> >> The only non-obvious card in the system is an MDB DR11B... is this a
> >> parallel interface?
> >Probably. MDB boards were usually named by their DEC counterpart.
> Seems plausible that it is a 16-bit parallel I/O card, from the 74173s
> attached to the headers. Anyone know whether this is DRV11-B compatible
> (it is a qbus card, of course), or otherwise have any programming
> information for it? From time to time I'm tempted to buy some old PeeCee
> just to get a usable parallel port, but I'd much rather use a PDP-11 :-)

Well, the software is much easier on the PDP-11 since there is usually
adequate documentation. Also, even when the PDP-11 hardware
and software was at its peak around 1982, the next generation of boards
and software was still compatible with the old programs and OS. With
the PC, everything seems to change every other year. Plus, even with
the old PDP-11 hardware, it seems to still last longer than PC hardware.
And from an I/O point of view, I hear that the interrupts on the PDP-11
are far better than what the PC hardware does.

So the only real advantage in using the PC seems to be the speed and the
size of the memory and the available disk space.

Sincerely yours,

Jerome Fine
Received on Sat Aug 05 2000 - 21:16:12 BST