Newsgroups: comp.arch
Path: utzoo!henry
From: henry@zoo.toronto.edu (Henry Spencer)
Subject: Re: Multiprogramming the Microcode: The B1700
Message-ID: <1990Oct14.001905.19442@zoo.toronto.edu>
Organization: U of Toronto Zoology
References: <1990Oct4.001346.4139@Stardent.COM> <8052@scolex.sco.COM> <2926@sequent.cs.qmw.ac.uk> <1990Oct11.164904.12550@zoo.toronto.edu> <27843@bellcore.bellcore.com>
Date: Sun, 14 Oct 90 00:19:05 GMT

In article <27843@bellcore.bellcore.com> mo@messy.UUCP (Michael O'Dell) writes:
>I think the Burroughs B1700 was multiprogramming at the microcode
>level before the Alto. ...

True, although with a somewhat different flavor.  The B1700 didn't have
the Alto's multiple microcontexts, which made microprogram context
switching effectively instantaneous and permitted using microcode
to supply most of the smarts for most of the i/o devices.  (For example,
the original disk interface had a one-word buffer and no DMA, and the
video generation hardware was at a similar level of non-complexity, with
carefully polished microcode doing all the work.)  The Dorado, and perhaps
some of the other Xerox D-machines, copied this approach, but nobody else
has that I'm aware of.
-- 
"...the i860 is a wonderful source     | Henry Spencer at U of Toronto Zoology
of thesis topics."    --Preston Briggs |  henry@zoo.toronto.edu   utzoo!henry