What is the purpose of memory in a computer?

Hard-drives store large amounts of data for extended periods of time. RAM stores smaller amounts of memory only while it is needed. Data stored in RAM can be accessed much faster than data stored in hard-drives. This is necessary because the processor can only interact with a few numbers at a time. An example might be when running a game - all the most necessary game data is loaded from the hard-drive into RAM. Then, as the game runs, the processor rapidly pulls small bits of data from RAM, performs calculations, and then quickly passes it back. The results are then displayed (through the video card) on the screen.