When you are using your computer, you may suddenly see that the C drive is red, or the system prompts that the C drive is full, which will affect the operation of the system. Cleaning the cache alone can only temporarily alleviate the problem, not fundamentally solve it. Look at other drives, there is still a lot of space. How to allocate unallocated disk to C drive? This article summarizes two solutions for you. The first is to use Win10's disk management, and the second is to use Partition Assistant.