Which HDD to use?
I have a 2tb caviar green 3.0gbs drive (5400rpm) and I have a 160gb 3.0gbs (7200rpm) drive. Everything is currently installed on the 2th drive. Should I move the OS to the 160gb drive or will I not notice a difference at all? Thanks!
While in general a faster spindle speed is desired for better(lower) access times.
The 160 gig drive is most likely from the days before PMR(The bits are standing and not laying down so to speak) and so will have very slow sequential read/write speeds.
You can perform a read test on the drive with HD Tune(Non Pro. If you use pro do NOT use a write test as it erases the drive.)
I would almost guess that the newer "slower" drive still has an edge. That said, if files are kept close to the outer edge of the large drive, you will also improve access times(does not show up on benchmarks, but it should help).
Now a modern Black or even Blue would crush the GREEN drives.