Transistor-Transistor Logic

(TTL) A common semiconductor technology for building discrete digital logic integrated circuits. It originated from Texas Instruments in 1965.

There have been several series of TTL logic:

 7400:	10 ns propagation time, 10 mW/gate power consumption,
	obsolete;

 74L00:	Low power: higher resistances, less dissipation
	(1 mW), longer propagation time (30 ns);

 74H00: High power: lower resistances, more dissipation: less
	sensitivity for noise;

 74S00: Schottky-clamped: faster switching (3 ns, 19 mW) by
	using Schottky diodes to prevent the transistors from
	saturation;

 74LS00: Low power, Schottky-clamped (10 ns, 2 mW);

 74AS00: Advanced Schottky: faster switching, less
	 dissipation, (1.5 ns, 10 mW);

 74ALS00: Advanced Low power Schottky (4 ns, 1.3 mW).

For each 74xxx family there is a corresponding 54xxx family. The 74 series are specified for operation at 0 - 70 C whereas the 54 (military) series can operate at -55 - 125 C