Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!utgpu!dennis
From: dennis@utgpu.UUCP
Newsgroups: comp.arch,comp.unix.wizards,comp.os.minix
Subject: Re: pdp-11/55
Message-ID: <1987Oct11.163617.1192@gpu.utcs.toronto.edu>
Date: Sun, 11-Oct-87 16:36:17 EDT
Article-I.D.: gpu.1987Oct11.163617.1192
Posted: Sun Oct 11 16:36:17 1987
Date-Received: Mon, 12-Oct-87 20:42:48 EDT
References: <1755@ncr-sd.SanDiego.NCR.COM> <275@usl>
Reply-To: dennis@gpu.utcs.toronto.edu (Dennis Ferguson)
Organization: Mechanical Engineering, University of Toronto
Lines: 44
Xref: utgpu comp.arch:2425 comp.unix.wizards:4478 comp.os.minix:1777
Checksum: 30538
Summary: Chronology not quite correct

In article <89@piring.cwi.nl> jack@cwi.nl (Jack Jansen) writes:
>
>I'll tell what I know, in roughly chronological order.
[...]
>	11/780	First VAX. Basically an 11/04 with an extra 32
>		bit processor and lots of extra busses. Also slightly
>		more expensive.
>	11/03	LSI version of 11/04. First Q-bus machine. The Q-bus
>		is a poor-mans-unibus: multiplexed A/D lines, only
>		one level of interrupts, etc.

The chronology is quite rough here.  I think the 11/03 might have been
available as early as 1973 or 1974.  I definitely saw my first one in
1976, a year or two before 11/780's were sold (indeed, the console
subsystems in 11/780's include an 11/03).  I remember this well,
that 11/03 was the first computer I ever wanted to take home.  I
eventually did, but much later, I use the CPU as a paper weight.

The Q-bus had 4 interrupt request lines from the beginning, like the
Unibus, though the 11/03 only supported one level.  The Q-bus did (and
still does) only have one daisy-chained interrupt acknowledge line,
however.  I think the latter is the reason why the microVax always sets
the processor priority to spl7() when servicing an interrupt (and why
the clock on early Ultrixes loses time) no matter what the bus priority
of the requesting device is.  You can't tell for sure what the priority of
the device which ends up taking the interrupt is.

>	11/23	LSI version of 11/34 with Q-bus.

But with 22 bit addressing.  I remember cutting traces on old peripheral
cards which used a couple of the new address lines as grounds so I could
run an 11/23 in 22 bit mode and use the extra memory as a RAM disk for
RT-11.

>	11/74	LSI version of 11/70, with qbus.

I think this is really an 11/73.  And it probably wasn't exactly like
an 11/70, it took years before DEC software would actually let you
run a separate I/D space program, even through the same OS would do
this fine on an 11/70.
--
Dennis Ferguson
Mechanical Engineering
University of Toronto