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Re: Creating grub/grub2/grldr.mbr bootrom with makerom


From: Yoshinori K. Okuji
Subject: Re: Creating grub/grub2/grldr.mbr bootrom with makerom
Date: Sat, 22 Dec 2007 09:06:32 +0100
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On Friday 21 December 2007 20:04, Robert Millan wrote:
> How well does compression work for GRUB 2 ?  core.img is already compressed
> (with lzo); if LZMA makes better results perhaps it'd be a good idea to
> switch.

It's not that simple. LZO was chosen instead of gzip, because of the size 
requirement on PC. To preserve safety, we need to keep the core part less 
than 31.5KB (63 sectors).

The size is the sum of non-compressable bootstrap code, decompression code and 
compressed code + data. When I made an experiment in PUPA, although gzip had 
a better compression ratio, due to the decompression code size, LZO won.

I don't know precisely, but I suspect that decompression code for LZMA would 
be slightly larger than gzip's (IIRC, a range coder is likely to require more 
code and data). So I don't expect that LZMA can replace the current usage of 
LZO in normal PC so easily.

Okuji




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