According to the right click "Get Info" on my 512GB SSD in my MBPr on Moutain lion I have used 50GB of the 256GB partitioned for MacOS (the other 256 is for Windows 7). Under the "Size" field in "Computer" in Finder it shows as 121GB. I've used Disk InventoryX and it it showing the drive as half full in the main view, but rough math of adding up the top 10 file types by size adds up to 45GB with the remaining types being only a few MB each (all under 100). Is there something I fundamentally dont understand here? I have TimeMachine backing up to an external HD (80GB on last backup) which 80+50 is 120. Which is close to the value shown in finder. Any thoughts/insights/ideas? Many thanks in advance!