The earliest computers to be commercially sold were made in the early 1950's.
They were enormous, consisting of several large wardrobe size cabinets,
using thousands of thermionic valves (not transistors), generating a lot of heat.
There was no keyboard, mouse, or screen as we know it now (2000 AD).
Information on early mainframe computers was entered either on:
paper-tape or
punch-card.
Output could be either on paper-tape or punch-card or on
continuous listing.
produced on High Speed Line Printers.
In the late 1960s virtual memory was implemented and
interactive computing was introduced when input/output was
via computer terminals.