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From: rokicki@navajo.STANFORD.EDU (Tomas Rokicki)
Newsgroups: net.micro.atari16,net.micro.amiga,net.micro.68k
Subject: Re: 68000 Memory Managment
Message-ID: <828@navajo.STANFORD.EDU>
Date: Thu, 11-Sep-86 15:46:34 EDT
Article-I.D.: navajo.828
Posted: Thu Sep 11 15:46:34 1986
Date-Received: Fri, 12-Sep-86 22:12:37 EDT
References: <508@elmgate.UUCP> <64@mit-prep.ARPA> <510@elmgate.UUCP> <79@mtxinu.UUCP>
Organization: Stanford University
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Xref: mnetor net.micro.atari16:1916 net.micro.amiga:4635 net.micro.68k:1212

In article <79@mtxinu.UUCP>, ed@mtxinu.UUCP (Ed Gould) writes:
> >> I hate to tell you folks, but Andy Bechtolsheim here at Sun has a patent 
> >> (applied for and granted) on using the untranslated addresses as the 
> >> RAS addresses and doing the MMU address translation before the column 
> >> addresses are needed for CAS.
> >
> >How the hell can the patent office grant patents like this?  It's sort
> >of like patenting the idea of grounding DTACK on a 68000 or putting
> >chocolate ice cream in root beer; the idea is too obvious.  To coin a
> >phrase, it's patently ridiculous.
> 
> If it's so obvious, why didn't anyone think of it before Andy did?

Let's look at this for a minute.  You have the following problem:

) you want virtual to physical address mapping
) standard practice is to map only the high order bits
    (this predates Andy by a good long time)
) virtual to physical mapping takes some time
) you want to use dynamic rams
) dynamic rams require half of the address, and then, some
    delay later, the other half
) Gee, Wally, what do we do now?

It's not that nobody thought of it before, but nobody patented it.
It's not a clever idea; it's the only reasonable solution.
I had a design like this for the 6809 and dynamic memory before the
68000 even came out; I just never built it.

It bothers me that such ideas can be patentable.  When you design
a new machine, these patents can restrict your design space; if they
start patenting all the good solutions to common problems, what do
we have left to design with?

-tom