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From: alex@umbc4.umbc.edu (Alex S. Crain)
Newsgroups: comp.sys.3b1
Subject: Re: XINU now available for 3B1
Message-ID: <1991Jun13.161510.17619@umbc3.umbc.edu>
Date: 13 Jun 91 16:15:10 GMT
References: <3057@public.BTR.COM>
Sender: newspost@umbc3.umbc.edu (News  posting account)
Organization: University of Maryland Baltimore County
Lines: 49

In article <3057@public.BTR.COM> thad@btr.btr.com writes:
>The following item just appeared in comp.archives.  Since I don't recall
>having seen any prior mention of it here in comp.sys.3b1, I've reposted it.
>
>Anyone know what this means?  Mt. Xinu sources for the 3B1???  (And, yes,
>I know that ``Mt. Xinu'' is ``UNIX (tm)'' reversed end-for-end :-)

	And to think that I seriously considered tossing my xinu books
recently, my my.

	The XINU referred too in the article is not Mt. XINU (commercial
MACH based BSD4.3 for assorted machines) but rather Douglas Comers XINU 
operating system. I haven't looked at XINU in some time, so this is all 
from memory.

	XINU is a multi tasking OS that was originally designed to be
downloaded onto a PDP-11 over a serial line. The idea is that you would
attach your PDP to a host, download XINU and a program image, type "go"
and watch it run. The image could then create more processes, talk to
a terminal, or whatever.

	XINU is multi tasking, but doesn't support virtual memory. Instead,
it works like mach threads, running different processes in the same address
space, allocating a piece of stack to each process. XINU handles the 
context switching and resource allocation (memory, semaphores, devices ...).

	This implementation is pretty minimal, sporting only a serial driver
and a line clock interface (to burp the context switch 60 times a second),
but the hooks are there for other drivers. XINU comes with a sample disk
driver, it shouldn't be too hard to swipe the disk driver code from the
diagnostics disk source.

	One of the most appealing things about XINU is the text written
by Dr. Comer for his OS class at Purdue, which describes, in detail, the
XINU design philosophy and details all the XINU procedures. Its well 
written and very complete.

	I may use XINU for a project that I've been working on, and I'd be
interested in hearing from anyone who does anything with the code. I 
recommend it strongly to anyone who wants to study operating systems, I'll
post an ISBN for the book when I dig up my copy.

	It would be a good thing if the code found a home in the archives.

-- 
#################################		           :alex.
#Disclaimer: Anyone who agrees  #                 Systems Programmer
#with me deserves what they get.#    University of Maryland Baltimore County
#################################	    alex@umbc3.umbc.edu