16 Bit Adder

Now we build the actual thing which will be used in an ALU. Assuming we have a 16 bit bus, we would need to add 16 bit numbers. So we probably need to add 2 numbers such as these:

Notice that the 2 LSB's can be added using a half adder, but after that there may be carry bits, so we will need a full adder for the subsequent bits. So this means that a 16 bit adder can be implemented using 1 half adder, and 15 full adders. If a carry bit is generated at the MSB position, it will be ignored.