Earlier in this chapter, I talked about how the CPU and other components inside your computer produce a lot of heat. The fan attached to the CPU and heat sink move hot air away from the processor. The power supply also has a fan, but you still have to get that hot air out of the case and replace it with cooler air from outside. In other words, the computer must have some kind of ventilation system.
That's why your computer's case probably has some air holes on the front, back, or sides. There might also be one or more fans mounted inside, next to a hole in the cover. A fan can be either a cooling fan that pulls air into the case and across the sources of heat, or an exhaust fan that pulls warm air out. Some computers might have one or more of each.
Unfortunately, the same ventilation system that carries fresh air into the case also pulls in dust and dirt. So your computer case might have some kind of dust filter next to the air intake holes. If your case has a dust filter, remember to examine it every few months and clean it whenever it becomes clogged with dust or dirt.
If your case doesn't have a filter, there's probably a layer of dust and crud on the blades of the fan, the floor of the case, the motherboard, and every other horizontal surface. A computer can collect dust bunnies just as effectively as the space underneath your living room sofa. Anytime you have the top off the case, it's a good idea to remove as much dust as possible with a vacuum cleaner, a small brush, or a can of compressed air.
Make sure the power is not connected when you clean out the dust.
The power and data cables inside your computer can also interfere with air flow. If you can, move as many cables out of the way as possible. This is especially true of the flat ribbon cables that connect disk drives to the motherboard-if you replace them with inexpensive round cables, you can allow air to circulate much more easily.