Bell Laboratory's engineers - John Bardeen and Walter Brattain - invented the transistor in 1947 and announced the invention in 1948. The junction transistor was invented by their associate, William Shockley, a few months later, and all three jointly shared the Nobel Prize in Physics in 1956 for their invention.
Transistors were also more reliable than vacuum tubes. Changing from the vacuum tube to the transistor paved the way for making smaller, faster and more efficient computers. There has been many different designs of transistors but they are primarily made of different layers of materials deposited on a silicon subtrate, thus the name Silicon Valley for the concentration of manufacturers in Calefornia.
Miniaturization is still continuing to this day. The university of Mancester's Transistor Computer, is believed to be the first one and built in 1953 with a CPU speed of 58MHz. Some of the computers of the Second Generation were:
1. IBM 1620: Its size was smaller as compared to First Generation computers and mostly used for scientific purpose. (about the size of a refrigerator)
2.IBM 1401: Its size was small to medium and used for business applications.
3.CDC 3600: Its size was large and is used for scientific purposes.