Page "Logic gate" Paragraph 9

The output of one gate can only drive a finite number of inputs to other gates, a number called the ' fanout limit '.

Also, there is always a delay, called the ' propagation delay ', from a change in input of a gate to the corresponding change in its output.

When gates are cascaded, the total propagation delay is approximately the sum of the individual delays, an effect which can become a problem in high-speed circuits.

Additional delay can be caused when a large number of inputs are connected to an output, due to the distributed capacitance of all the inputs and wiring and the finite amount of current that each output can provide.