A:Answer I did some comparisons between the drives, and it would appear from WD's website, Mainstream HDD's sometimes come with a variable speed rating to compensate for power usage and heat. In laymen's terms, the drive is capable of 7200 rpm, and will use it when it has to, otherwise it will spin down to a lower rate when idle. It also improves on the life span of the drive. There is also sometimes a difference in warranty, but with these two drives, they are the same. 2 yrs on parts (limited) and labor.
