Early computer cases were little more than boxes that sat on the desk and served as monitor stands. Today, some manufacturers build "designer" computers that come in fancy colors and command premium prices.
The real value of a case does not lie in the label, color, or how pretty it looks. The case houses all the internal components, offers access to the outside world (ports and connectors), and protects the PC's delicate circuits from damage and electromagnetic interference. And it protects surrounding devices, such as TVs, from the PC's EMI.
Electromagnetic interference (EMI) is a newer term for radio frequency interference (RFI). EMI is any radio frequency that is emitted from an electrical or electronic device that is harmful to the surrounding equipment or that interferes with the operation of another electrical or electronic device. A computer interferes with radio, telephone, or TV reception when it generates EMI. Any high-quality computer will contain special circuits and grounding to prevent emissions into the surrounding area. Running a computer without its cover is a sure way to generate EMI.
As computer technicians, we don't usually concern ourselves with the computer case; we simply deal with whatever our customer already has. However, when it comes to recommending a computer for purchase, the size and configuration of the case should be considered. Depending on the business application, the difference between a tower and a desktop design could be important.
When considering the case, there are three general rules to follow:
- The bigger the box, the more components it can hold (the greater the expansion potential) and, often, the better the airflow (essential for cooling). Large cases are easier to work with.
- The more compact the box, the less expansion potential it has; working on it is often much more difficult, and usually airflow is reduced.
- Smaller cases that come with a power supply usually have lower wattage, once again reducing the number of internal devices that can be installed.
It is not a good idea to run a computer for extended periods of time with the case open or removed entirely. This not only produces EMI, but also results in improper airflow and reduced cooling of the system components.
Working with Cases
In any repair job that involves inspecting or replacing internal components, the technician has to open the case. That used to be very simple; the technician would remove four screws in the back of the computer with a Phillips screwdriver, then pull the case's covering shroud forward to reveal the contents. Today, however, cases come in a variety of forms, with screws in the front or back, fancy plastic bevels in front, and featuring one of several types of metal wraps-some in several parts, some in a single piece.
The majority of cases still open the old-fashioned way. But if you find yourself with one of the exceptions and can't locate screws in the back, check to see if the plastic cover in the front can be pulled off. If so, that should reveal three or four screws. Then see if the main cover can be pulled forward. If not, look for screws that secure one or more of the side panels. Some side panel designs are great for granting easy access to our next topic, motherboards. This style of case allows one to inspect or remove the motherboard without having to remove the entire outer covering.
The following points summarize the main elements of this lesson:
The case of the PC defines the size, shape, and configuration of the motherboard, the amount of expansion possible, and the space into which hard drives and other internal accessories can be fitted.
To prevent EMI and ensure system components are properly cooled, you should avoid running a computer without its cover.