coapp-developers team mailing list archive

[Garrett Serack <garretts@xxxxxxxxxxxxx>]

Hey Olaf,

MSI actually doesn't *directly* support compression at all.

Files can be embedded in the MSI or embedded in a CAB file that is embedded in the MSI. Depending on the tool used to create the MSI, the files may or may not be in a compressed CAB file, and the CAB file itself has three options for file compression (LZX, DEFLATE and PAQ)

Deflate should be about the same as zip--it's the same compression algorithm.

LZX is actually a very good compression algorithm, and often beats zip, rar2, and others. It's specifically tweaked to store x86 binaries, so theoretically should produce the best results.

It's important to note that content outside the embedded CAB files are not compressed (so any data/metadata in the MSI tables for example) and that it's probably compressing that pretty good (that data is often a lot of text, and should compress well).

And, FYI: MSI examination Tools like Orca (from the Windows SDK) transparently unpack CAB resources, and so you don't even see them--which until I found that out, I thought that they weren't being compressed at all!

G

Garrett Serack | Open Source Software Developer | Microsoft Corporation 
I don't make the software you use; I make the software you use better on Windows.


-----Original Message-----
From: Olaf van der Spek [mailto:olafvdspek@xxxxxxxxx] 
Sent: Wednesday, August 11, 2010 10:22 AM
To: Garrett Serack
Subject: MSI compression

Sometimes I see .msi inside .zip, with compression being 7%. Is the compression of .msi that bad?
Garett, maybe you could ask the MSI guy?

Olaf