RAM Usage Display: Free, Cached, Used

Notes about RAM usage on computer:

• Free RAM: 
• The amount of RAM never been used
• Cached RAM: 
• The amount of RAM ever been used to load programmes, but OS doesn't want to free them, OS keeps them to avoid loading programmes from disk again.
• When free RAM is not available, OS will throw away some of the Cache RAM to make free space for allocation.
• Used RAM: 
• The amount of RAM allocated to programmes, can't be used for other ones.