I have this HD for a half year now. Just reinstalled Windows and it shows up like 149Gb. That is correct because capacity is 160Gib...
BUT, it also shows up that my HD has 122Gb free space. Windows installation with SP2 and many AutoCAD 2008 is taking 6Gb. That would be total = 128Gb.
If the total capacity is 149Gb where the hell is those 21.2Gb!? I searched a lot of hardware forums and didn't found solution.
Here is screenshot from WinDirStats app, that is really useful and showing that unallocated 21.2Gb :
I had similar problem once. I installed Partition Magic and it found those 21Gb unallocated and I jsut merged it with C: partition. The problem is, this time, Partition Magic shows it is REALLY used:
This is freshly installed OS with newest drivers. Before installation I formated partition from Recovery Console.