HD #s dont make sense with Vista Image Backup

For the first time I did a "Complete Windows and PC backup and Restore Image" (Vista Ultimate) to a WD external HD (160GB) (which I did format but still showed a capacity of 150 gigs under properites). Vista indicated that the image would require 37 gigs...that seemed correct as the C drive showed about 32 gigs used and the RECOVERY D drive has just under 6 gigs. But upon successful completion of this backup, I see it shown that there is 131 gigs free out of a total of 150...or is it 160GB? in this external HD...so only 19 gigs was required for this first image using Vista backup. What am I missing?

 

Well, regarding 160 vs. 150 you can read more here. Basically a 160GB HD is 160 GB in the decimal sense, not 160 GiB in the binary sense.

And for the 19 gigs actually used vs 37 gigs Vista told you about, Vista uses ZIP compression when backing up files to use less space, so the 19 gigs are actually those 37 gigs compressed. I guess Vista told you 37 gigs because that's the worst-case scenario - where none of the data can be compressed.

 

Thanks Jim. I forgot about the compression. The "imaging" feature that come with Vista Ultimate is sweet and simple. Long overdue.

 

Yea, about 15 years overdue.