Memory
Our memory is responsible for allowing our computer to do all sorts of complex calculations at rates faster than a human possibly could. The more memory we have, the more things we can do at once and the faster we can do it. This applies for all of the programs that our computer has to use when it's being run, from a calculator, to a game.
We generally have two types of memory, cache memory and RAM (Random Access Memory).
Cache Memory is the faster of the two and is located closest to the CPU in our computer. The CPU is what is doing our calculations, therefore the closer we are to the CPU, the faster our calculations. The problem with cache memory is that we have a lot less of it then we do of RAM. This means we want to perform as much calculation in cache memory as we can before resorting to RAM in order to be as fast and efficient as possible. We also have several layers of cache memory, the closest one labelled "L1" while the others being L2, L3, etc. L1 is the fastest layer while the others get progressively slower.
Random Access Memory is the slower of the two and located farther away from the CPU. However you can have much more of this kind of memory, and can frequently be seen in large 1-8 Gigabyte sticks now, with multiple of them on one computer.