<Tr> <Td> Computer buses </Td> <Td> Short range </Td> <Td> RS - 232, SCSI, PCI, USB </Td> </Tr> <Tr> <Td> Long range (computer networking) </Td> <Td> Ethernet, ATM, FDDI </Td> </Tr> <P> A general purpose computer has four main components: the arithmetic logic unit (ALU), the control unit, the memory, and the input and output devices (collectively termed I / O). These parts are interconnected by buses, often made of groups of wires . Inside each of these parts are thousands to trillions of small electrical circuits which can be turned off or on by means of an electronic switch . Each circuit represents a bit (binary digit) of information so that when the circuit is on it represents a "1", and when off it represents a "0" (in positive logic representation). The circuits are arranged in logic gates so that one or more of the circuits may control the state of one or more of the other circuits . </P> <P> When unprocessed data is sent to the computer with the help of input devices, the data is processed and sent to output devices . The input devices may be hand - operated or automated . The act of processing is mainly regulated by the CPU . Some examples of hand - operated input devices are: </P>

When was the computer invented and by whom