Subject: Re: Test kernel available
To: None <>
From: Johnny Billquist <bqt@Update.UU.SE>
List: port-vax
Date: 01/16/2001 16:38:00
On Tue, 16 Jan 2001, Brian Hechinger wrote:

> Michael Kukat drunkenly mumbled...
> > 
> > VAXen are the successors of the PDPs, the majority of VAXen having a real bus
> > use the same QBus as the smaller PDPs did. Only very new VAXen use the
> this i pretty much knew.  i've got a PDP-8e and i used to own a VAX 11/730 and
> they were strikingly similar.  in fact, i pulled some boards out of the /730
> (never booted, so i don't know if it worked or not) and they are marked LSI-11!!
> (early QBus) which makes me ask: can i use LSI-11 cards in QBus or did someone
> stick those cards in that machine for "storage only"?

The PDP8/e boards use something called Omnibus. The cards share the form
factor with Q-bus cards, but not the electrical stuff, so don't try to
move cards from one system to the other...
Unibus (used in large PDP-11s and older VAXen) also have cards in the same
form, but uses yet another electrical layout.

Q-bus is Q-bus. A VAX, DECstation or PDP-11 with Q-bus have the same bus.
You can use the same peripherials, and so on. What might be worth knowing
though, is that older Q-bus PDP-11s have the memory on the Q-bus as well.
Also, the very first gerenation of Q-bus stuff only had 18 address wires,
so if you find something really old Q-bus, it might need some extra

> > TurboChannel (VAXstation 4000 series). But there are also BI, XMI and some
> > other buses out there in the VAXen.
> never even heard of BI, although XMI rings a bell for some reason.

VAXBI is a fuller name, I believe. Both were used in newer mid- to high
range VAXen.

> > Look at the assembly language: VAXen are more relates to PDPs, they are CISC
> > machines. DECstations are RISC machines and only exist due to DEC didn't get
> > the Alpha CPU finished in time AFAIK.
> they share CPUs don't they (the KA series were used in the larger PDP machines
> like the -11 and -12, yes?)

Hmmm. A short crash course on DEC nomenclature perhaps...
CPUs are called Kx where x is some letter. Thus you have a PDP-11/70 CPU
which is called a KB-11C, while a VAX8600 CPU is called a KA-860. A PDP-10
CPU might be called KA-10.

The PDP-11 and the PDP-12 have nothing in common, and are very different
sizewise as well. The PDP-12 was a 12-bit architecture evolving from the
PDP-8 (which in turn came from the PDP-5). This series is definitely
RISCy, even though it was developed in the '60s. The PDP-11 is rather

The PDP8/e CPU is called a KK8-E.

So, there is no such thing as a KA series, and "larger" PDP machines is
also confusing, and you should definitely not group the PDP-11 and PDP-12

If we were to talk about large PDPs, then we are talking PDP-10. A PDP-11
is a *small* computer compared to that. (Heck, most VAXen are small
compared to PDP-10s)
Also, they are very different beasts from all points of view. You had one
implementation of the PDP-10, the KS-10 CPU, which was used in a
Unibus-based DECsystem, the -2020. But apart from having a Unibus, it had
nothing in common with a PDP-11. The PDP-10 is a 36 bit machine, while the
bus and addressing is 18 bits. The Unibus can handle 18 bits, and the
PDP-11 uses that as 16 bits plus two parity bits.

I hope I'm not boring anyone... :-)


Johnny Billquist                  || "I'm on a bus
                                  ||  on a psychedelic trip
email:           ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol