If we want to resize a harddisk partition in Windows XP, we have to make use of 3rd party software such as GPartEd. In Windows Vista and Windows 7, there is built-in utility for us to resize the harddisk partition.
We seldom need to resize the harddisk partition, but most new computer pre-installed with the OEM OS is partitioned as one big partition only, although the harddisk can be of terrabytes of capacity.
One practical usage of this is to split the big C: drive into two. This will make possible system backup and system imaging of C: to D: drive in another partition.
You might also want to perform partition resizing when one of your harddisk partition is almost full, while there are space in other partition to squeeze out. In this case, shrink the partition with excess storage, and extend the partition which is almost full.
Here is how to do it in Windows 7.
Open the Start Menu, right click on Computer and select Manage. Then, expand Storage on the left panel, and click on Disk Management.
Right click on the partition you want to resize.
You will be given options to extend, shrink or delete the selected partition (a.k.a. volume). Of course, you can't extend a partition if there is no empty partition space next to it, and you can't delete a primary partition with extended partition(s) unless you deleted all the extended partitions first. Beware that deleting a partition will cause total data lost in that partition.