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In article <2187@wpi.wpi.edu>, lfoard@wpi.wpi.edu (Lawrence C Foard) writes:
> 
> Why isn't parallel computing used more? I can't think of many problems...

Most people quote Amdahl's Law which essentially says that some portion of a
program is sequential in nature and the amount of time it takes to execute
that sequential code is the lower limit on the amount of time it will take
the program to execute.  Other's have disagreed, saying that you would
rewrite the program (eliminating the sequential code) for parallel systems.
This lead to Mohler's law which said that you'd scale up the parallelizable
part of the program and solve larger problems.

There are real parallel systems out there.  The Cogent XTM system from 
Cogent Research is one example (of a distributed memory system).

For around $20K you get two Inmos T800 transputers each with 4 Mbytes of
RAM, a 90 Mbyte hard drive, an 800K floppy drive and a 1024 by 808 by 256
grey scale monitor.  However the most important thing about the system
is that it is scalable!  You can attach a "resource server" with more
processors (and memory).  The operating system has built into it a
communication system called "Linda" which makes parallel programming
much easier than other parallel machines.  The operating system is
highly compatible with Unix System V.

The future of computing lies in parallel programming.
 
John Roberts
johnr@ogccse.ogc.edu