One of the panels on the System Dashboard has caused some concern for users. This panel is the Memory Usage Panel. It looks like this:
Having a high Cached Memory Usage is actually a good thing. It means your system is using this space to store running some types of running processes. Without this being cached then the system would have to create new processes frequently.
Real Memory Usage is the actual amount of RAM usage. This should ideally be low. Having a high percentage of real memory usage is normally cause to investigate what’s wrong.