Today's picture shows an early radio receiver. The device was self contained, and capable of receiving a signal from across the country. You can see that the device is based on seven vacuum tubes and the bottom half is filled with batteries. A vacuum tube was a very early electronic component that could act as a switch or an amplifier. They used lots of power, and burned out frequently. In the 1970's the vacuum tube was replaced by the solid state transistor. A transistor could do all the work of a tube as a fraction of the cost, low power and they did not burn out. Using transistors miniaturized electronics for two reasons. First, the transistors themselves are small, and second, since they dont use much power, the need for huge batteries was reduced. For comparison, modern computer chips can have in the neighborhood of 10 billion transistors.