[Joe Forster/STA]

What is the real and compressed size of that maxi image? The two should tell us the compression ratio.

However, Windows has to be able to "virtual-uncompress" the file contents on the fly. Especially, seeking around such a compressed file must be a bitch! For this reason, I think, the compression ratio cannot be as good as with an archiver (although ZIP has a relatively good compression ratio and it compresses/uncompresses extremely fast, too!) and/or the file must be compressed in separately uncompressable chunks and there must be some kind of an index added so that the "virtual-uncompression" can be started from the beginning of a chunk, rather than the beginning of the file, upon every seek.

[Edit] Hmmm, I've tried the Need for Speed: Most Wanted maxi image by Team Riverstorm: 1.74 Gigabytes real size, 1.23 Megabytes compressed size. By compressing it, I won 1.74 Gigabytes of hard disk space. I think, the amount of free space, reported by Windows, is the actual amount of space left on the drive; no estimations, concerning the ratio of compressed files, is made. If you save uncompressed files onto the drive, the amount of free space will be reduced by the total size of the files saved onto it. However, if you save compressed files, the reduction of free space will be less than the total (uncompressed) size of the files saved.

@XtremeX: Stupid question: Have you enabled compression, in general, for the drive? Although, if you haven't, why would Windows let you enable compression on the file level?!