Path: utzoo!mnetor!tmsoft!torsqnt!lethe!yunexus!ists!helios.physics.utoronto.ca!news-server.csri.toronto.edu!bonnie.concordia.ca!uunet!crdgw1!crdos1!davidsen
From: davidsen@crdos1.crd.ge.COM (Wm E Davidsen Jr)
Newsgroups: comp.arch
Subject: Re: 64-bits, How many years?
Message-ID: <3209@crdos1.crd.ge.COM>
Date: 19 Feb 91 17:47:12 GMT
References: <9102171510.AA24745@lilac.berkeley.edu> <1991Feb18.163010.31688@m.cs.uiuc.edu>
Reply-To: davidsen@crdos1.crd.ge.com (bill davidsen)
Organization: GE Corp R&D Center, Schenectady NY
Lines: 39

In article <1991Feb18.163010.31688@m.cs.uiuc.edu> gillies@m.cs.uiuc.edu (Don Gillies) writes:

|                                        So we conclude that because
| 64-28 = 36, it will take 120 years to outgrow the 64-bit address
| space.  

  We may never run out of 64 bits of address space. That's not to say we
won't have problems larger than that, but there's a real possibility
that some limitations of physics will hold us back.

  The first is that size of an electron, and the minimum size of a
trace. A trace has to be a certain size, or it ceases to be a conductor
and becomes an exercise in probability. Therefore you can only downsize
a chip so far, even in theory. Given that limit, and the relatively low
speed of light relative to increasing clock rates, it may never be
practical to build a computer with all the memory 64 bits will address,
ignoring the engineering and financial problems.

  Now the reason I say "may" never run out, is that other technology may
be developed, although I don't think it will be an extension of anything
we have today. Optical is size limited by the size of the photon, and is
still limited by the speed of light. Mark that one off as a candidate
for ultra dense computing.

  How about using isotopes of individual atoms for bits? Let's use
hydrogen, since the atoms are small. We add a neutron to the atom for a
1, remove it for a zero. Of course if we have an error and keep
adding... we get a new meaning to the term "program blowup." Well, okay,
I'm kidding, but the external stuff to diddle atoms is likely to be
larger than the atom, so this is unlikely, too.

  Therefore, I conclude that the speed of light makes 64 bits likely as
the largest physical address space we will even need. I have lots of
faith in new development, but I have faith in relativity and physics,
too.
-- 
bill davidsen	(davidsen@crdos1.crd.GE.COM -or- uunet!crdgw1!crdos1!davidsen)
  "I'll come home in one of two ways, the big parade or in a body bag.
   I prefer the former but I'll take the latter" -Sgt Marco Rodrigez


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