Mercury delay line is a kind of storage devise used in early computers, when crystal valves were not invented and electronic valves need too much energy. The idea of storing signals by delaying was raised. Under the instruction of this idea, mercury delay line was invented.
The main idea goes like this. A sound wave needs some time to go through a pipe filled with some certain medium. In such a period of time, the information within the sound wave is stored in this pipe. If we can keep the sound wave going in the pipe forever, the information is forever stored. However, people need to ensure the quality of the sound wave. Therefore, before the sound is sent into the pipe again, it needs to be magnified and clarified. By doing the emit, receive, clarify, and reemit process, the information is stored.
Each pipe like that with a length of 1.5 meter and diameter of 1 centimeter filled with mercury is called a channel, which can store ten 91 bit number, about 0.1 Kb. Interestingly, over 1 ton mercury is needed for such a storage we feel neglectable. In one of the earliest computer project UNIVAC, ten channels were used. In order to keep the whole system working stably, the temperature need to be kept at 40 degree centigrade.
Today, crystal valves are playing an important role in computer memory, and the size and energy cost of a computer is strongly reduced. Though sound base delay lines have exit the world of computers, they were still widely used in radar field. Modern computers have a memory of 16Gb, which is about 1000000 times the memory of the earlies computers. Technology is developing faster and faster. While enjoying the gift from advanced technologies, we should not forget the work of former pioneers and the basic rule of nature, especially sound here.