A few weeks ago I ordered a 2TB WD Caviar Green 3.5" internal HDD for my Mac. The model I received was a WD20EARX-00PASB0 6Gbs 64MB. I ordered another yesterday from a different supplier thinking I was getting the same model, but this time the model I received was a WDBAAY0020HNC-ERSN 32MB. I don't see any reference to this model on the WD website so I'm assuming it's an older model. In real world situations, what differences will I notice between the above two drives? I bought one to use on a daily basis for reading stored music and video data, and the other to used as a one-off backup of this data and stored off-site. If the 64MB cache version has faster access times, I should use this as the daily access drive, but does this bear out in reality or is the 64MB cache a moot point given that the drive only spins at 5400rpm? Please note that my knowledge of HDD design is near to zero so apologies if my questions don't make sense!