Date   : Mon, 06 Mar 2006 23:51:28 +0000
From   : Jules Richardson <julesrichardsonuk@...>
Subject: Re: Warning: Sad case on list!

Fragula wrote:
>  A *real* pdp-11 (note case here) would in my mind be an 11/70 fully
> loaded except the "MMU" upgrade (can't remember what that was called)
> with an ASR-33 w.punch/reader, some VT-52 and VT-100's (which I do
> have!) twin dectapes and a couple of 9-tracks for luck. 

Ahhh yes. Our 570's much like that, with three washing machine-sized CDC 
drives and all the trimmings. The separate memory crate's having an off moment 
  these days (the machine had been stored for ten years totally dismantled, 
unlabeled, and spread across ten rooms, so it's wonder we managed to find all 
the bits at all) but it will run again at some point.

Runs a very early hypertext-like system, from a time long before the web had 
been invented...

> Mine is a nice
> little thing though, and runs on single phase.

They pretty much all were I think; you could wire them for three phase but all 
the ones I've stumbled across have been single phase. Even our 570 is and 
that's big by pdp standards.

Not sure about the DECSystem 10 and 20 machines though as they were bigger 
animals still (no chance we'll ever get hold of one - last UK one in 
commercial hands was removed over ten years ago)

On the big pdp front, NATS down at West Drayton had 120 11/34 crates chained 
together doing processing until last year when they dumped them all - it was 
sad to see the big empty room where all the cabs had once stood. (we did 
rescue some nice stuff from them though, and we've got more 11/34's than we 
know what to do with as it is!)

> has some flakey RAM,

Sounds familiar!

In the various manuals on bitsavers there should be all sorts of memory diags 
you can load in which can help identify the duff chip.

> I've started working out a simplified, essentially updated clone of
> the ACW SCSI adaptor (which works fine with anything that works with
> standard ADFS).

Oh, that was the other thing... not sure if the Acorn adapter supports parity, 
and lots of drives can't be jumpered to ignore it. Blah, we had this 
discussion just a few months back on here and I can't remember what the 
outcome was - and the schematics aren't to hand at the mo to check :/

> on a BBS. "Old ST-225's dont die, they just get noisier!" (and stiction,
> but thats fixable.)

Seem to remember ST225s are really prone to cooking one of the power ICs on 
the board...

> Whether you got the address decoding right, ;-> and how this will fit in
> on a fairly busy 1MHz bus (a buffered "eurocard" type box of some sort,
> on the end of a long "wedge feeder" cable, is probably where I'm going
> to end up.

You need a Cube Eurobeeb... backplaned beeb goodness :-)

Bugger - to other Mike: I suddenly remembered I have that spare CU beeb bus 
extender for you... busy busy at the mo but give me a prod next week and I can 
stick it in the post for you if you still want it...


cheers

Jules