Output stage of LM 311 is different from a typical Op Amp line 741. This modification enhances the flexibility of LM311. It has two outputs. Pin 7 is the positive output and forms the collector of the NPN output transistor. Pin 1 is the negative output that forms the emitter of the output transistor. Usually pin 1 is grounded to allow collector-emitter flow of current. Since the positive output is the collector of the output transistor, it is current sinking. Normally in the off state, the collector of output transistor is pulled to Vcc .The output transistor saturates when its base gets more than 0.7 volts. When this happens, the output is pulled to emitter voltage. That is the load turns on when the output goes low. In typical Op Amps, the output is current sourcing and gives current when the output becomes high.