PS3 Drive Swap Question

[zxvfrr41]

Okay, I swapped out my 60Gb drive for a WD 320Gb drive last night. I had about 8Gb of space left on the 60Gb. When I performed a backup prior to the drive swap, it said it backed up 32Gb of data. So that's my first question.

60Gb total space - 8Gb remaining = 52Gb of data on the drive. The backup was 32Gb. What's the other 20Gb? The OS can't take up 20Gb because weren't the early PS3's 20Gb?

Onto my second question. I installed the 320Gb WD drive, formatted the drive, and then restored my backup. When I check the System Settings, it shows 225Gb / 298Gb, meaning there's 225Gb of free space out of 298Gb. Why doesn't it show 320Gb or something close instead of 298Gb? And how could there only be 225Gb of free space? That would mean there's 73Gb of data (298-225) on my PS3. How is that possible considering I had a 60Gb PS3 to begin with and it's the same data?