The power supply does exactly what its name suggests: It supplies power to the rest of the components in the computer. The power supply takes 120 or 240 volts (depending on the country you are in) of alternating current from your electrical outlet and converts it to 3.3 volts, 5 volts, and 12 volts of direct current. It contains a number of leads that supply different voltages for different types of devices (such as floppy drives and hard drives).
Adapter cards allow you to adapt your computer to another role, such as controlling assembly line robots, or to add specific functionality to your computer, such as printing. The most common adapters are now integrated into most motherboards. These components include display, network, keyboard control, mouse control, serial ports, parallel ports, and USB ports.
With the first computers that came out on the market, most of the elements (if not all of them) were added to the motherboard by using the adapter slots, such as ISA, PCI, and AGP (well, ISA anyway, since the other slots did not exist).
Cooling system and fans
As electricity moves through any circuit, heat is generated, which is illustrated by looking at a simple circuit that contains an incandescent light bulb. As electricity moves through the bulb, the filament heats to glowing. Heat is also generated as electricity moves through the integrated circuits that are contained in most of the components of the computer. In addition to these fixed integrated circuits, hard drives contain moving parts that generate heat from friction. These components generate a large amount of heat, which needs to be removed from the critical components to prevent them from failing early in their careers.
To remove heat from computer systems, there has been a steady increase in the use of fans, vents, and other heat dissipation units. Heat sinks with fans are commonly placed on processors and critical chipsets. Heat sinks are heat conductive metals (usually aluminum or copper), which have a solid side in contact with the chip that they are protecting, and thin fins on the other side, putting greater surface area with the air, to dissipate or transfer heat to the air. The use of a fan with the heat sink allows more cool air to flow through the fins. Case vents and fans bring cool air into the computer housing and to vent and pull hot air out.
Faster processors produce more heat. As processors have become faster, more methods for pulling the heat away from the processor have been developed.