What is a LM339 Ic?

A LM339 is a small scale integrated circuit(SMIC) that contains 4 "Norton"* comparotors on a single chip. The LM339 is not universal as most Operational Amplifiers are. The comparotors on the chip do not amplify with feedback, rather only switch state(+V, Ground) on their output. The benefit to the "locked" behavior is some of the smallest power drains a TTL chip can provide and fast switching speeds. *Norton denotation indicates that the op-amp/comporator operates from a single suply rail(+V,Ground), where normally you would expect to use a dual supply rail for op-amp/comparators(+V,Ground or V_(same thing), -V).