The beginning In the early 1940s some of the first programmable machines started to appear in research labs such as Harvard Computation Lab or Bell Labs. These machines were glacially slow by today's standards. However, they were also very difficult to program, and to operate. Programming required intimate knowledge of the machine, and often required resorting to hacks in order to make the computations run faster. Speed was always critical. During this time, when the US was at war, most of these machines were used to compute missile trajectories, damage coverage from bombs, and other war-related computations. Machines such as the Mark 1 were often used 24 hours per day, 7 days of week. The human effort for keeping such machines functional was split between programmers, mostly responsible for developing programs, and operators, which would be ensure the machine was functional throughout the computation. They would repair or replace relays or other components. In some machines, such as the ENIAC, operators would be required to step in during a computation, for it to continue (e.g. flip switches or perform certain electric connections).

Speed In around 80 years, computers went from 3 (numerical) operations per second (on the Mark 1), to 1 billion instructions per second on A15 bionic chips. This means that one second of computation from your average mobile phone would have taken around 10.5 years to complete on the Mark 1. The success of today's machines can be largely attributed to the major advancements in hardware, with the emergence of the silicon technology. The success of today's software however, is a testament to our ability to build abstractions that make programming easier.

Complexity