In previous chapters we studied actual I/O and secondary storage devices: tubes, tapes, disks, cards, mice, touchscreens, lightpens, ... the list seems endless. Now we will discuss how the CPU manages to collect actual values from these devices for internal storage and use.

The earliest computers had separate input and output instructions. In those days (very late 40s, early 50s) peripherals, input and output devices and secondary storage devices, were few in number and crude. Usually there was a printer and a punched card reader and a tape drive. The tape was often used for both programs and data. In fact, the essential system software managed tapes, directing when to load a particular tape on the tape drive. These were called TOS (Tape Operating Systems). Imagine how slow and clumsy they were!