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Bipolar transistors, and the gates built using them, were the dominant digital hardware from the switch from vacuum tubes in the late 1950s until their replacement by CMOS in the early 1980s.

'Bipolar' simply refers to the construction of the transistors, using three layers of 'positively' and 'negatively' doped semiconductors in a 'sandwich'.

The first bipolar logic family was resistor-transistor logic (RTL), followed by the improved diode-transistor logic (DTL), and finally transistor-transistor logic (TTL).