In the early days of computing, CPU time was expensive, and peripherals
were very slow. When the computer ran a program that needed access to a
peripheral, the CPU would have to stop executing program instructions
while the peripheral processed the data. This was deemed very
inefficient. The first computer using a multitasking system was the
British Leo III owned by J. Lyons and Co..
Several different programs in batch were loaded in the computer memory,
and the first one began to run. When the first program reached an
instruction waiting for a peripheral, the context of this program was
stored away, and the second program in memory was given a chance to run.
The process continued until all programs finished running.
Multiprogramming doesn't give any guarantee that a program will run
in a timely manner. Indeed, the very first program may very well run for
hours without needing access to a peripheral. As there were no users
waiting at an interactive terminal, this was no problem: users handed on
a deck of punched cards to an operator, and came back a few hours later
for printed results. Multiprogramming greatly reduced wait times when
multiple batches were being processed.
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