The basic purpose of memory—human or machine—is to keep a record of information for a period of time.
The basic purpose of memory—human or machine—is to keep a record of information for some time. One of the noticeable things about human memory is that it's extremely good at forgetting. That sounds like a major defect until you consider that we can only pay attention to so many things at once. In other words, forgetting is most likely a clever tactic humans have evolved that helps us to focus on the things that are immediately relevant and important in the endless clutter of our everyday lives—a way of concentrating on what matters. Forgetting is like turning out old junk from your closet to make room for new stuff.
Computers don't remember or forget things the way that human brains do. Computers work in binary (explained more fully in the box below): they either know something or they don't—and once they've learned, barring some sort of catastrophic failure, they generally don't forget. Humans are different. We can recognize things ("I've seen that face before somewhere") or feel certain that we know something ("I remember learning the German word for cherry when I was at school") without necessarily being able to recollect them.
Unlike computers, humans can forget...remember... forget... remember... making memory seem more like art or magic than science or technology. When clever people master tricks that allow them to memorize thousands of pieces of information, they're celebrated like great magicians—even though what they've achieved is far less impressive than anything a five-dollar, USB flash memory stick could do!