When you partition your hard drive you end up creating two or more virtual hard drives. What it does is takes you HD and puts in 'markers' of some kind that tell programs that there are actually two hard drives.
A lot of people, including myself, partition their hard drive and have one partition for data and one for the OS and program files. By doing this, if you end up reinstalling windows you don't loose all your data if you reformat.
Multiple partitions also allows you to load more than one operating system off of the same physical drive.
<b>Just because I like AMD or Intel more at a time because of one product compared to another, does not make me a fan boy, it makes me a person who is able to make a descision for myself.</b>