On a single silicon chip, known as a microchip, sits the central processing unit. or CPU, that different programming instructions ‘soft wire’. A microprocessor becomes a microcomputer when interfaced with memory and input-output devices. The Intel 4004, earliest microprocessor, had a 4-bit data bus, addressing 4.5 kilobytes of memory. The Intel 8080 that in 1973 cost about $400 was the first mass produced microprocessor.