Path: utzoo!attcan!uunet!mcsun!ukc!dcl-cs!aber-cs!pcg
From: pcg@aber-cs.UUCP (Piercarlo Grandi)
Newsgroups: comp.arch
Subject: Re: 64-bit addresses
Summary: Patents are not so easy...
Message-ID: <1654@aber-cs.UUCP>
Date: 22 Feb 90 02:14:15 GMT
Reply-To: pcg@cs.aber.ac.uk (Piercarlo Grandi)
Organization: Dept of CS, UCW Aberystwyth
	(Disclaimer: my statements are purely personal)
Lines: 42

In article <38764@apple.Apple.COM> baum@apple.UUCP (Allen Baum) writes:
  
  First of all, IBM has patents on their particular implementation of a
  reverse map MMU.  This does not imply they invented it, nor does it

They hve *very* wide ranging claims. Remember also that this is the company
that spent millions of dollars advertising their discovery of virtual memory.

  imply that they believe that they invented it, nor does it mean that
  can do anything to anyone who wants to publish a paper about it.
  
  Secondly, if you can prove that you worked on something and that it
  was in the public domain prior to when IBM claimed they invented it
  (public domain in this context means that it was not kept a trade
  secret, I believe), then you can actually invalidate IBMs patent
  claims, should they conflict.

Yes, spending a few hundred thousand dollars. IBM, if they cared about their
patent, could sue *me*, conceivably, to protect it, if I made such a claim.
  
  Thirdly, I'd like to see the paper...

Not so easy. You join a long queue of people to which I promised a copy
of some paper or other (mine or otherwise). Don't hold your breath. :-(.

  Note that IBMs implementation is a straight reverse map; it comes with a
  'hash anchor table' bit of indirection first, which presumably improves
  performance. This may be a bit of non-obviousness which makes the patent
  really valid.

That's the scary thing. I could not get hold of the IBM patent (all the info
I know comes from a Byte article on the ROMP), but the two key points of my
design are an (actually two) hash table to randomize access to the TLB (an
idea I got for another application, from Prof. Ian Watson of Manchester
University), and an optional indirect token table to support efficiently
segment sharing (yes, you can do that with a reverse map MMU, but it
requires a *very* subtle idea).

-- 
Piercarlo "Peter" Grandi           | ARPA: pcg%cs.aber.ac.uk@nsfnet-relay.ac.uk
Dept of CS, UCW Aberystwyth        | UUCP: ...!mcvax!ukc!aber-cs!pcg
Penglais, Aberystwyth SY23 3BZ, UK | INET: pcg@cs.aber.ac.uk