Have you ever got the message warning you are running out of space on Windows 7, or low disk spacer alert when booting system? If you received that information you probably using computer frequently, since new disks will often reserve much more free space for later use. However, Windows 10 upgrade is approaching or maybe it has already landed on your pc. Free space is become less and less which encourages you to free up disk space.
What is your first thought on fixing C partition low disk space problem? Is it delete file in C drive program files or move any large files? Before you do that, we suggest you not to do so, because it's helpless, files in C partition are mostly related to system boot or running, it's risky to manage files in this partition when you are not very familiar with each document.
Disk Management in Windows 7 is a useful tool to distribute disk space as a default partition manager. If data on D drive is not much, you can delete D partition at first, to make free space, which is displayed as "Unallocated space" when running Disk Management. Then expand C drive by adding that allocated space, then reload the disk map, you can see the low disk space alert is gone. So, let's make a summary, first delete D partition, and then add free space to C Drive, that's how Disk Management works on how to extend C Drive partition. But, what if D partition cannot be deleted?
As we mentioned above, what if D partition cannot be deleted, how can we extend C drive.
We'll try Shrink Volume in Disk Management to see what will happen. Click on shrink volume in D partition; make some unallocated space from it. The theory is to use this space to expand C drive, but Extend Volume is grayed out in C Drive, it cannot be clickable. The theory is right, but the unallocated space position is not right. It's not right behind C Drive, it's the reason extend volume gray out.
Partition Extender will extend C drive on no conditions. No matter the position is right or wrong, have or have no unallocated space, it will definitely extend C Drive.