uVAX II Memory Board

From: Megan <mbg_at_world.std.com>
Date: Sat Feb 3 22:43:08 2001

>I was sort of hoping (dreaming) that someone has noticed these 8 Mbyte
>boards going to sleep and the PDP-11 still looking for additional
>memory. I realize it is probably impossible, but how does the 11/83
>manage to use both the Qbus for disk I/O and the PMI for memory?
>And if the PMI memory is below the CPU rather than on top, the 11/83
>reverts to an 11/73.

As I understand it, the VAX only communicates with the memory over
the cable. On the 11/73 and family, the original memory reference
goes out on the bus, and the initial response is over the bus, but
several additional words are then supplied over the PMI bus... so
those words are cached in expectation of them being referenced due
to proximity to the actual referenced word.

>Didn't you once make a (very small) disk memory out of some old DEC
>memory board? Or was that normal Qbus memory but at a high address
>with a gap from the regular memory.

What I did was take one of the Bridge86 boards (an 8086 on a Qbus
board with its own memory) and wrote a handler to access its memory
as if it were a disk).

>What would it take to build a small interface that looks like the HD hard
>disk from E11 as far as an actual hardware interface is concerned?
>Could it loop right back into this uVAX II memory board via the 50 pin
>header on top? Since the Qbus interface is already there in the
>backplane, maybe that interface could be added to the 8 Mbyte of memory?
>See, I said I would ask dumb questions!

Actually, that is an idea I mentioned in mail earlier tonight, prompted
by something Zane said, I think...

I was thinking that if the MS6xx memory boards only use the Qbus for
their power, and all transactions really do happen over the cable, then
it should be possible to design a Qbus option which looks like a disk, but
which communications with one or more MS6xx boards over the PMI cable.

Is there an actual signal requirement for the MS6xx boards to be in the
PMI slots of a qbus backplane, or is it simply because they are closest
to the uVax processor board...?

                                        Megan Gentry
                                        Former RT-11 Developer

| Megan Gentry, EMT/B, PP-ASEL | Internet (work): gentry!zk3.dec.com |
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Received on Sat Feb 03 2001 - 22:43:08 GMT

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