The digits that are stored in each are the same, but the use of each type of memory is different. RAM, or volatile memory (as the previous poster stated), is used to temporarily store data that is being used while the machine is powered on. Once you shut off the machine, however, the volatile memory is wiped clean and starts fresh the next time the machine is powered on. SD cards, hard drives, flash drives, etc. are used to store data. These two things are completely separate entities in computing, but equally as important.