Path: utzoo!mnetor!uunet!husc6!bloom-beacon!gatech!hubcap!acornrc!glassman
From: acornrc!glassman@ames.arc.nasa.gov (Steven Glassman)
Newsgroups: comp.parallel
Subject: Amdahl's law(s)
Message-ID: <1354@hubcap.UUCP>
Date: 11 Apr 88 14:47:35 GMT
Sender: fpst@hubcap.UUCP
Lines: 23
Approved: parallel@hubcap.clemson.edu


I have seen (and heard) lots of mentions of Amdahl's laws, but never a
concrete source for any of them.  Did Amdahl really invent (or even say) these
laws?  Or has he become a legend like the unlucky (law generating) Murphy?  

I have heard of at least two laws of parallelism attributed to him.  "Amdahl's
First Law" gives the potential speedup of a parallel program based on the
number of processors and the fraction of parallel work available.  "Amdahl's
Second Law" (which my reference admitted isn't due to Amdahl and that he
didn't even believe it) gives limits on the amount of speedup in a parallel
program as the number of processors and the program size grow linearly.

Yesterday, I heard a new law attributed to him.  This one related the amount
of I/O to the MIPS of the processor (unfortunately, I don't remember it 
exactly, but it was something like: one bit of I/O per ??? per MIP).

Anyway, this is a request for a collection of Amdahl's laws and sources for 
these laws.  They can't all be legends.

Thanks,
Steve Glassman

{decwrl|ames}!acornrc!glassman