"High memory usage" means the internal Random Access Memory (RAM) is inadequate. It has nothing to do with your hard drive. The answer for that is to add more memory to the computer.
Defragmentation reorganizes the hard drive so all of the files are contiguous, saving the time the disk would take skipping over the surface to pick up file fragments.
To defrag a disk:
Start/Computer/Right Click the drive you want to defrag
Select Properties/Tools/Defragment Now/Defragment
Answered Mar 08, 2012
Edited Mar 08, 2012