What Is The Relation Between Installed Ram And Used Space On My Hard Drive

I removed 8 GB RAM from my computer, then C drive shows 20 GB used space. So I think that RAM memory is taken by C Drive. After I re-installed 8 GB RAM, it will shows 28 GB used space.

Is there any reason for that? I know there is no relation between RAM and the physical memory, but why it is showing like this? Please tell me that what is the reason.