If you wish to create a partition (in which to install Ubuntu Linux, for example) on a hard drive which already contains a Windows partition, or if you need to provide more space in an existing partition that is running out of space, you will need to perform one or more partition resizing operations. You can re-allocate hard drive space from one partition to another, or add previously UnallocatedSpace to a partition.
Resizing Windows Partitions requires special attention and is accomplished in a manner different from that used to resize other types of partitions.
When shrinking a partition containing data, attention must be given to the amount of free space left in the partition; especially a Windows partition, but true for any filesystem. The less room left in a partition, the more likelihood of fragmentation of files, and the harder it will be to defragment that partition.
Rule of Thumb: Leave at least 10% free space on any partition to reduce fragmentation and make defragmentation easier.
Note that, in order to expand a partition, you must have free space next to it in which to expand. This can be accomplished either by shrinking another partition next to it, or moving a (or some) partition(s) away from it. See the Moving A Partition page for details on moving a partition.
See notes in Additional Notes on Partitions on the Operating Systems And Primary/Extended Partitions page for additional restrictions on resizing operations.
To resize a partition, first make sure the partition is unmounted. If the partition is mounted, most of the options in the menu will be unavailable, except for one that says "Unmount," which you should select to unmount the partition.
Notice in the image that the partition I am resizing is the Windows NTFS partition that covers the entire hard drive, which I created earlier. A new Windows computer's hard drive will typically be formatted in this manner; one large partition covering the entire drive.
Once you are sure the partition is unmounted, right click on the partition you wish to resize and select "Resize/Move" from the menu as illustrated above. You will then be presented with the following:
Resizing a partition can be done one of two ways:
Dragging and sliding. Position the cursor over the arrow on either side of the graphical bar shown in the screenshot, left click and hold, then drag the arrow; away from the edge for shrinking or towards the edge (into the free space, if available) to expand it.
Changing the "New Size" or the "Free Space Preceding/Following" sizes. This can most easily be done by changing the size of the partition itself. This is done either by using the up/down arrows to the right of the "New Size" window, or by directly editing the size itself in that Window. Alternately, you can shrink the partition by increasing the non-zero side of the partition in either the "Free Space Preceding" or "Free Space Following" window.
If you attempt to expand the partition by decreasing the non-zero side of the partition ("Preceding" or "Following," depending on where the free space is), it will move the partition instead of increasing it's size. The same will apply if free space exists on both sides of the partition. See Moving A Partition for details.
After changing the size of the partition, just click the "Resize/Move" button, and the changes will be recorded and visible in a window at the bottom. When you are sure that you have resized it as you desire, you click the "Apply" button at the top and the partition will be resized. Your hard drive will then be as follows: