Re: 21 bits ...

From: Nelson H. F. Beebe (
Date: Fri Feb 23 2001 - 12:19:07 EST

Since folks are debating whether 21 bits is really enough for Unicode
forever, I thought I should toss in these gems from my quotation
collection, about previous mistakes when people thought something was
big enough:

There is only one mistake that can be made in computer design that is
difficult to recover from---not having enough address bits for memory
addressing and memory management. The PDP-11 followed the unbroken
tradition of nearly every computer.
C. G. Bell and W. D. Strecker\\
1976 % Hennessy and Patterson p. 481

A partial list of successful machines that eventually starved to death
for lack of address bits includes the PDP-8, PDP-10, PDP-11, Intel
8080, Intel 8086, Intel 80186, Intel 80286, AMI 6502, Zilog Z80,
CRAY-1, and CRAY X-MP.
David A. Patterson and John L. Hennessy\\
1990 % p. 481

Pitfall: Extending an address space by adding segments on top of a
flat address space.\\[1ex]
\ldots{} From the point of view of marketing, adding segments solves
the problems of addressing. Unfortunately, there is trouble any time
a programming language wants an address that is larger than one
segment, such as indices of large arrays, unrestricted pointers, or
reference parameters. \ldots{} In the 1990s, 32-bit addresses will be
exhausted, and it will be interesting to see if history will repeat
itself on the consequences of going to larger flat addresses versus
adding segments.
John L. Hennessy and David A. Patterson\\
1990 % p. 483

I haven't a similar quote about 32-bit IP addresses, but IPv6 (see RFC
1883) notes `` IPv6 increases the IP address size from 32 bits to 128
bits, to support more levels of addressing hierarchy, a much greater
number of addressable nodes, and simpler auto-configuration of

- Nelson H. F. Beebe Tel: +1 801 581 5254 -
- Center for Scientific Computing FAX: +1 801 585 1640, +1 801 581 4148 -
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