What is the difference between Ram and Hard drive?

Ram and Hard disc both are different from each other.The purpose of hard drive is to store data permanently until we want it to remove.The ram is to remember the stuff, whenever we open too many applications or softwares on the system the ram remember it.If the ram has high storage power then we can open too many applications (at the time running other apps), if the ram is low then can't have the access to open too many apps at the same time.The ram needs the electric power to remember while the hard drive works on the magnetic plate.If we power off the system then the data will still be on the hard drive.In the case of ram this is totally different as if we power off the system and turn it on again the apps we opened before will not still be open as before, we will need to run that applications again.