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From: cjp%megatek.UUCP@ucsd.edu (Chris Pikus)
Newsgroups: comp.os.research
Subject: Cache theory question (UNIX)
Message-ID: <1456@darkstar.ucsc.edu>
Date: 24 Feb 90 02:59:38 GMT
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	The Unix disk buffer cashe is organized as
a combination of both a hash table and a linked list.
that is there several linked lists and which one to use
is determined by a hashing function.

	To wit, when one wishes to access/add a particular block
in the buffer cache, the kernel performs a hashing function
on BLKNO (usually a mod( 17) i beleive) and then walks down
the that list to find said BLKNO.

	My question is thus: WHY mod 17???

	I know the answer is fairly obvious, since 17 is 
a prime number, there would more likely to be an even
distribution amongst the lists. If something like a filesystem
started to have certain things regularly spaced, they might have
a tendency to "resonate" adn fill up one list if one used a number
like 16.

	To be more precise, is there any reason they picked 17, and
if so, is there any supporting documentation/articles/mathematical_treatises?
Could they have picked any prime (like 29, or 53, or 2011)?

	I know this is a pretty esoteric question but I was 
curious and I know there is a lot of UNIX historians on the net.

	Thank you very much,
	Christopher J. Pikus