The second generation computers saw the replacement of the vacuum tubes by transistors. A transistor can be thought of as a switch, but with on moving parts. Because of high speed operation in microseconds and were capable of storing tens of thousands of characters. Manufacturers began producing business oriented computers with more efficient storage and faster input and output capabilities. Second generation computers were reliable, compact in size and virtually free of heat problems.
The first computer was made in 1946 at the University of Pennsylvania. ENIAC (Electronic Numerical Integrator And Computer) contained 18,000 vacuum tubes, it was 30 tons heavy and occupied the space of 154 m2
