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Re: lynx-dev DOS port of bzip2

From: David Woolley
Subject: Re: lynx-dev DOS port of bzip2
Date: Sun, 10 Jan 1999 18:16:41 +0000 (GMT)

> I am not sure what you mean by "locality of reference". Did you try the
> program? I don't see more paging to disk than with many other programs
> (I run a pentium 75 with 8 Meg of memory).  In general, I think it a bad
> idea to change defaults, unless required by a system constraint.

With the default compression, a 6MB Linux system is not big enough to 
avoid thrashing without -s and is certainly not capable of compressing 
without thrashing at the the default compression level.

The thing that has made the bzip compression schemes possible is the large
amounts of physical memory on modern machines.  In the default configuration,
bzip2 sorts a 900,000 element array, and requires several bytes for every
element in that array.  -s reduces the number of entries on compression
and uses an algorithm which trades size against speed for decompression

These are the figures from the man page:

             Compression:   400k + ( 7 x block size )

             Decompression: 100k + ( 5 x block size ), or
                            100k + ( 2.5 x block size )   [ -s ]

which indicate that you need a working set of 4.6MB without -s to decompress
and 6.7M (excluding the code and operating system code).  That means that
if you have less than 8MB you are at risk of thrashing.  4MB is plenty to
run MS-DOS or even Win3.1.

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