Colossus also featured limited
programmability.
When the allies invaded North Africa in 1942, they discovered that the firing tables they used to aim their
artillery were off. This resulted in requests for new ballistics tables that exceeded the ability to compute them.
John Mauchly and J. Presper Eckert used this opportunity to propose the development of an electronic high-speed
vacuum tube computer. Even though many experts predicted that, given the number of vacuum tubes in the
machine, it would only run for five minutes without stopping, they were able to obtain the funding to build
the machine.
Under a cloak of secrecy, they started work on the machine in the spring of 1943. They completed
their work on the machine in 1946. The result was the Electronic Numerical Integrator Analyzer and
Computer (ENIAC), a machine that weighed 30 tons and was built using 17,468 vacuum tubes and 6000
switches. The machine was more than 1000 times faster than any machine built to date. Unlike modern
computers, reprogramming ENIAC required a rewiring of the basic circuits in the machine. ENIAC heralded
the dawning of the computer age.
10 INTRODUCTION TO COMPUTER SCIENCE [CHAP. 1
Figure 1-8 The first computer bug
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