"The hard disk is simply the slowest part of the computer system. CPU’s can transmit data in the form of gigabits per second, memory bandwidth goes over 5GB/s and graphics cards can handle data in the order of 38GB/s across its memory buses. But the trusty hard disk in most cases cannot deliver sustained data faster than about 60MB/s, simply put, going for the faster CPU isn’t going to be able to speed up your load times on games if you can’t get the data off the disk quickly enough.
In recent years, the advancement of the hard disk has started to become a major part of the PC industry with Serial ATA replacing the older Parallel standard that was used for over 10 years. Native Command Queuing or NCQ for short sped up the way the data is read off the drive, and now with perpendicular recording coming into the frey from companies like Seagate, we are now starting to see speed increases as much as what a magnetic recording device is capable of."