Indeed, there has never been a defragmentation utility in the different versions of OS X, and there is still none in Yosemite. I will not explain what the cause of
SSD or HDD: Which is Better for Your Specific Needs?
While there are merits to both the Solid State Drives(SSD) and Hard Disk Drives(HDD), deciding on the one that best suits your needs can be pretty tough. Each of the