Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!utgpu!water!watmath!clyde!rutgers!gatech!bloom-beacon!mit-eddie!ll-xn!ames!amdcad!sun!gorodish!guy
From: guy@gorodish.UUCP
Newsgroups: comp.arch,comp.unix.wizards,comp.os.minix
Subject: Re: pdp-11/55
Message-ID: <32222@sun.uucp>
Date: Wed, 28-Oct-87 13:56:43 EST
Article-I.D.: sun.32222
Posted: Wed Oct 28 13:56:43 1987
Date-Received: Sat, 31-Oct-87 10:07:46 EST
References: <1755@ncr-sd.SanDiego.NCR.COM> <275@usl> <29933@sun.uucp> <15417@onfcanim.UUCP>
Sender: news@sun.uucp
Lines: 17
Xref: utgpu comp.arch:2576 comp.unix.wizards:4830 comp.os.minix:1876

> Another piece of trivia, and the reason the /45 was my favourite model
> of the PDP-11: the Unibus arbitrator ran even when the CPU was halted -
> it was a separate piece of hardware.  Thus, you could use the console
> switches to deposit cylinder and track addresses and a "read" command
> into a disc controller, and the data appeared in memory.  No boot code
> was necessary.  For other members of the family, the bus arbitrator
> ran only when microcode was executing, so you needed to be executing
> instructions (just branch-to-self would do) in order for DMA to memory
> to work.

I think this worked on the 11/34 as well; the instructions for bringing up V6
on an 11/34 with no console switches involved stuffing addresses and commands
into the RK05 controller's registers in order to yank the requisite blocks from
"/unix" and "/etc/init" in order to patch them and to write them back.
	Guy Harris
	{ihnp4, decvax, seismo, decwrl, ...}!sun!guy
	guy@sun.com