A Look Inside
The next step is to open the case to actually look inside the PC. Different PC case designs open in different ways, but it's usually a fingers-only exercise with newer PCs, and at worst, may require removal of a few screws. It's not hard at all.

To see what's really going on, we have to open the case. Most newer PCs require no tools. Instead, finger-operated clips and large thumbscrews make access a snap. (click image for larger view)

In most vertical "tower" or "mini-tower" case designs, the left side of the case (as seen when you face the PC from the front) is designed for easy removal. Here, we've set our test PC on what would normally be its right side, and are preparing to remove what's normally the left side of the case, now facing up for easy access. This Dell design is meant for tool-less access: The side panel is held in place with two squeeze-clips on the rear corners of the panel and one knurled screw in the middle of the panel's rear edge. In Photo 5, I'm pointing at one of the squeeze-clips, and you can see the knurled screw already loosened and protruding from the case on the right side of the photo. It's a "captive" screw; it can't be removed fully from the panel, so it can't be dropped or lost. You just loosen it until it turns freely, and leave it in place.

Most case-latching mechanisms are very simple, like these L-shaped slots. (click image for larger view)

There's no single standard way of removing a PC's side panel. The Dell's is held on by small teeth that engage L-shaped slots along the body of the PC: You slide the side panel straight back a short distance, then lift away from the PC body. In other designs, you pull the panel straight back all the way. Other panels are hinged from an edge, or pull straight out, and so on--just work carefully, and in good lighting, and you should be able to see how your side panel comes off.

If you've never opened a PC before, the jumble of wires inside may look intimidating. But we're here for simple cleaning, not re-wiring. (click image for larger view)

In this instance, the visible portions of this case interior don't look too dirty. I've seen instances where cases have been nearly filled with fluff, carpet fibers, pet hair, and the like. While this isn't the worst PC I've ever seen--not by a long shot--it definitely does need cleaning, as you'll soon see.

A closer look shows a light to moderate dust buildup on what's normally the bottom of the case; but still, this isn't an alarming amount of dirt--yet.

The closer you look, the more dust you'll find. (click image for larger view)

In this Dell design, a plastic shroud acts as an air duct between the CPU and the cooling fan on the back of the PC. This duct ensures that air drawn by that fan must pass over the CPU's heat exchanger first; in effect, concentrating the cooling airflow over the CPU. In other designs, the CPU has no shroud or ductwork. But where such ductwork exists, it must be removed so you can access the parts beneath it.

In most systems, the worst dust is on the fans and around the CPU; in this system, both are beneath this shroud. (click image for larger view)

Note: All the normal common-sense rules of working with electronics apply here: Work in a clean, well-lighted area. Make sure the PC is powered off and unplugged before you open it. Eliminate any static electric potential between you and the PC by touching an exposed part of the metal framework of the PC; and so on. If you're unfamiliar with these basics, see articles like this, this, or this; or how-to guides like this, this, or this. A Google search can turn up any additional information you may need.

This shroud is held in place with two snap-tabs; easily released with a fingernail or a small screwdriver. You unsnap the tabs, and the whole shroud simply lifts off. Other designs may use clips or screws, but the idea's the same.

The shroud is held on with two simple snap-tabs, and is easily removed with fingernails or a small tool. (click image for larger view)

Once the shroud is off, you can begin to get an idea where all the dust went.

The inside of the shroud offers a hint as to what lies beneath. (click image for larger view)

This is why the rest of the case was fairly clean: When the fan shroud concentrated the airflow over the CPU and heatsink, the dust and dirt in the air was likewise concentrated. This is by far the dirtiest place in this system. And note: Some systems will be much, much worse than this!

Even in clean workspaces, PCs pick up and astonishing amount of dust and dirt. (click image for larger view)