How do I use an "unallocated space" partition in Windows 7?

Unallocated

Fire up the disk manager (right-click Computer, click Manage and then click Disk Management), and I'm guessing that you're looking at something similar to this:

That line represents a single physical hard disk that is divided into three partitions:

• System Reserved - You may have something like this, a recovery partitions, or perhaps nothing at all.

• C: - This is the partition that contains your C: drive.

• Unallocated - This is the partition in question.

That unallocated partition represents disk space that will not be used until you allocate it. There are typically two approaches.

Format it as an additional drive

A very common approach is to simply create a new drive out of the unallocated space.

Right-click that Unallocated drive and click New Simple Volume...

This starts the "New Simple Volume Wizard". Click Next on the resulting dialog to be taken to the page where you specify the volume size:

The default answer is to use all of the available space, which is probably what you want. If you want to break the unallocated space into multiple drives, you might choose a smaller size.

Click Next and you'll choose the drive letter to be assigned to the new partition:

Once again, the default is probably appropriate, unless you have a specific reason to change it.

Click Next and you'll specify formatting options:

The answers to the default are typically appropriate, although this is a good time to specify the Volume label.

Click Next to get a summary screen for confirmation, and then Finish to complete the operation. Windows then formats the drive and when complete, it appears as "just another drive" on your system:

You can begin using the new drive immediately.

Expand the adjacent drive

The other approach, which in previous versions of Windows required third-party tools, is to simply expand an adjacent volume to use the unallocated space.

In our example, we'll right-click the C: drive, and click Extend Volume...

That option should only be available if there's room to expand - meaning that there's an unallocated partition following the C: partition.

This time, we'll start the "Extend Volume Wizard". Clicking Next takes you to the "Select Disks" dialog:

This somewhat confusing step is all about selecting which partitions on the disk are to be added to the volume that we're extending. The good news is that in this simple and common case - an unallocated partition immediately following the C: drive - the dialog is pre-loaded with default choices that are probably what you want: extend into the entire unallocated partition.

So all we need do is click Next.

A summary screen confirming our choice appears. Click Finish, and Windows begins the operation.

When complete, the unallocated partition is gone and the C: partition is larger: