Can Anybody Tell About The History Of Main Memory (RAM)?

For many years main memory was one of the most expensive components of computer components to manufacture. However, technology has revolutionized main memory components over the past 4o years or so. Their size has been drastically reduced and they have become less expensive as the manufacturing materials have changed from vacuum tubes to magnetic cores to transistors and finally to chips.
The earliest form of main memory was based on vacuum tubes. Today's technology can put 256K or 1 or 2 MB on a single main memory chip; the equivalent main memory capacity would have requires a shelf of vacuum tubes more then a mile long. And tubes were not reliable: their power requirements were high, they generated heat, they failed frequently, and they were slow. The transistor, invented in 1947, was much smaller and reliable provider of main memory. It also had smaller power requirements and failed less frequently than vacuum tubes.
However, the main memory of almost all computers today is based on semiconductor chip technology. Chips are very small and relatively inexpensive to manufacture, and they do not as much power as older forms of main memory. The use of chips has greatly increased the memory capacity of computers.