Generally, users of Windows prefer the zipping module embedded with Windows XP or WinZip software and hardly, require any other compression software until required otherwise. The situations may include the different file-format, like ".rar" for which the user requires WinRar from rarlab.com.
Now, 7-zip is free software that let's you deal with many compressing algorithms including the most popular one's zip and rar. However, only un-rar'ing is possible that is rar files can be extracted but can't be created. Including this is a new file format .7z in 7-zip which is their new open compression standard.
Here are some facts from the 7-zip publishers that will clearly state about the sound-ness of the algorithm
QUOTE
FILE SET: The Canterbury Corpus (11 files totaling 2,810,784 bytes, popular file set used to compression rates).
Archiver Compressed size Ratio
7-Zip (zip format) 676284 100%
PKZIP 2.04g -ex 726047 107%
WinZip 7.0 (Max) 731499 108%
CODE
Archiver Compressed size Ratio
7-Zip (zip format) 676284 100%
PKZIP 2.04g -ex 726047 107%
WinZip 7.0 (Max) 731499 108%
Another fact or datasheet is more interesting
QUOTE
FILE SET: The GIMP 1.2.4 for Windows after full installation (127 subfolders, 1304 files totaling 27,128,826 bytes). The GIMP is the GNU Image Manipulation Program. It can be downloaded from www.gimp.org.
Archiver Compressed size Ratio
7-Zip (7z format) 5445402 100%
WinRAR 3.10 6004155 110%
WinAce 2.3 6242424 115%
CABARC 1.0 6455327 119%
7-Zip (zip format) 9461621 174%
PKZIP 2.50 9842800 181%
CODE
Archiver Compressed size Ratio
7-Zip (7z format) 5445402 100%
WinRAR 3.10 6004155 110%
WinAce 2.3 6242424 115%
CABARC 1.0 6455327 119%
7-Zip (zip format) 9461621 174%
PKZIP 2.50 9842800 181%
These facts clearly states that 7-zip provides compression standard which far more better than existing one's and moreover, is freeware.
The only area where the software lacks is its interface though it is comparable to WinZip but not as intelligent as the WinZip's interface. However, it integrates seamlessly with the Windows shell providing right-click options to create archive or extract from archive.
I hope this will change your mind towards Open source stuff and you would like to try this new standard which provides more compression.

