Memory and Disk Space are not the same thing.A computer's memory is analogous to a human's brain. It's very fast so information comes up right away, but it is limited in its capacity. Humans invented writing and books to record more information than could be held in their heads and to share with one another. Along the same lines computers have disk space. It's much slower to access and requires more work to do so, but it can hold vastly more information and it's easier to pass on to others. You hand a book to another person while a computers can use a CD, DVD, thumb drive, etc to exchange information.