Historically, computers evolved from mechanical computers and eventually from vacuum tubes to transistors. However, conceptually computational systems as flexible as a personal computer can be built out of almost anything. For example, a computer can be made out of billiard balls (billiard ball computer); an often quoted example.[citation needed] More realistically, modern computers are made out of transistors made of photolithographed semiconductors. COUNT 3
QSN1 Vacuum tubes in early computers were replaced by what? ANS1 transistors QSN2 Transistors are typically made up of what today? ANS2 photolithographed semiconductors QSN3 A computer that is made using pool balls is known as what? ANS3 billiard ball computer)