They were big and impersonal. Then came personal computers. Now, a computer is no longer a single machine. We have computer families. The daddy computer talks to his daughters via the motherboard.
Nobody drives, they all take the bus.
Or the pulse train. Computers are sometimes like committees, they have several parts wasting time by doing the same thing at the same time. They argue a lot about who gets the front seat and who gets to drive. That's why they need bus arbitration. Cash memory is the part of the computer that remembers how much money you spent on your computer.