Upgraded from 20GB to 160GB Internal Hard Drive on PS3!

OK, let me first start by saying, it works! I got this drive from newegg:

http://www.newegg.com/Product/Product.asp?item=N82E16822136071

I got free 3 day UPS shipping but I guess that's over because now they want like $5 for 3 day shipping. Guess I lucked out in that respect.

OK now the question; After installing and formatting the new drive why does the PS3 list it as having 122GB free after formatting and not 159 something GB? Does the PS3 system use almost 40GB for internal operations?!?! That's bigger than the original 20GB drive!

Here is another strange thing, I backed up the original 20GB hard drive to an external 120GB USB hard drive I formatted with Swissknife v3.0 because of the XP/Vista 32GB FAT problem, (Swissknife is free and works great for FAT formats above 32GB!) and recovered it to the new internal hard drive once it was installed. The backup went well but 10GB of backup only took up 1GB on the new drive according to the PS3, I now have 121GB free instead of a freshly formatted 122GB after recovering the 10GB backup. Is this a PS3 software glitch?