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From: dewar@merv.cs.nyu.edu (Robert Dewar)
Subject: Re: Overflows (lisp fixnum-bignum conversion)
Date: 1997/04/07
Message-ID: <dewar.860441935@merv>#1/1
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References: <1997Apr2.202514.1843@nosc.mil>
 <Pine.SUN.3.96.970405054237.22894A-100000@eskimo.com>
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Organization: New York University
Newsgroups: comp.lang.ada
Date: 1997-04-07T00:00:00+00:00
List-Id: <comp.lang.ada>


Larry said

<<I don't see it going that fast.  Disks I use hold 1 GB, while others
can hold 4 or 9 GB.  64 bits allows me to address the contents of about
2,000,000,000 of the 9 GB drives.  How many disk drives have ever been
built ?>>

First, the 10GB drives you are used to using on small machines are by no 
means the largest storage devices in use to day, many large mainframe
installations approach terabyte storage capacity, and some exceed it.

Second, your calculation assumes that you are linearly mapping the disks
into memory, that's not at all the way it works, instead you would map
them into a hierarchical arrangemnent, allowing LOTS of extra space for
expansion in each node. The whole idea of a 64-bit address space is that
you can "waste" it lavishly to allow for growth of structures, and not
run out. 

For instance, in an Ada environment in a 64-bit machine, it makes perfectly
good sense to give every task a gigabyte stack, even if you have thousands
of tasks, but you cannot use this approach at all on a 32-bit machine.