Multiplexers and shift registers are integrated circuits that allow for more outputs to be available for use while also not using up as many pins. Multiplexers allow for both analog and digital inputs and outputs but they can only take in one input/output at a time. They are able to switch between the inputs and outputs very quickly. Shift registers will only take up three pins and can send/receive multiple bits of data at the same time. They have a slower response time and can only read digital inputs.
Berry College Physical Computing 2017 