RAM
CPUs can do math real fast, but they can't remember much stuff.1
This is what RAM is for. RAM stands for "random access memory." The random access part just means that a CPU can ask for any bit of info at any time.
Most computers nowadays have an even number of RAM sticks. This is for interesting reasons I don't fully understand.
1
In 8th grade I had someone physically hand me a piece of paper with their name and fun facts about them because I had kept forgetting their name the entire year. I don't know what Sam is up to now, but I remember that she likes pistachio ice cream.