What does Presario_RP (D:) low mean?

I am usaing a Compaq laptop and I am getting a message Presario_RP (D:) is very low

Well the D drive is usually either a backup drive used for restore points, or a disc drive. In your case, I'd say it's the former. I've never had restore points work properly for me, if I were you, i'd just remove it. Try right clicking on My Computer and checking the tabs there. I'm not on my PC right now so I can't check for exact names, but there's something there for disabling it.

To you very much for your help.
How do I disable it?
Should I buy a memory card for it and how much do they cost?