Display devices (mostly printers) were minimal, too. One story tells how programmers of the Univac I tried to draw maps on a printer that printed out only numbers, not even letters or punctuation!

Consequently, those computers had a PRINT instruction and a READCARD instruction. Since computers weren't shared, no one thought of any other way of doing I/O. However, programmers noticed that the huge discrepancy between the speed of the CPU and the speed of the peripherals meant that a computer system would do a flurry of many "operate" instructions (ADD, MOV, SUB, etc.) and then it would hit an I/O instruction. The hardware would have to pause until the I/O instruction completed, usually many milliseconds later. This wasteland of time would later become a fertile prairie upon which multiprogramming would flourish.