APU
These parts are the merry marriage of a CPU and graphics card. Using one of these essentially gives you one more card slot to work with. Like a normal CPU, it defines the architecture of the computer, and the number of components that can be connected to the computer before it stops working. In addition it also provides basic graphical capabilities.
Do note that due to the limited space on the chip, these CPUs are slightly slower than their "pure" equivalents, and provide comparatively low-fidelty graphics. So while the tier one APU can control as many components as a tier two CPU, it only runs as fast as a tier one CPU, and only provides the graphical fidelity of a tier one graphics card.