Adder

An adder is a collection of hardware (now gates) which, as the name implies, can add together the two numbers on its inputs.

The primary limit on the speed of an adder is the 'ripple propagation' of carries (consider the case of the case of the addition of 01 to 077777), which effectively sequentially stacks the delays across the entire adder. (This has been the case since the days of Babbage, whose machines implemented clever carry mechanisms.)

A number of 'carry lookahead' mechanisms have been devised to try and bypass the propagation delays inherent in sequential carries.