In earlier lessons, we provided an overview of the computer. In this chapter, we focus on the computer's infrastructure. We begin with the centerpiece of the computer, the motherboard, also called the mainboard. The motherboard is the key part of the hardware infrastructure. It is a large circuit board that serves as a home for the central processing unit (CPU) and all its associated chips, including the chip set and RAM (random access memory), and connects them to the rest of the physical elements and components of the computer.
The case, or chassis, which usually is made of metal, holds all the primary electronics of the personal computer (PC) and often all the drives as well.
After this lesson, you will be able to
- Identify the primary types of PC cases
- Explain how the case helps to protect the PC and surrounding devices from electromagnetic interference
To casual users, the PC is a metal container, attached by a few cables to a keyboard, mouse, and monitor. In fact, the case is more than just a box to house a computer.
The real value of a case does not lie in the label, color, or how pretty it looks. Instead, the case houses all the internal components, offers access to the outside world via ports and connectors, and protects the PC's delicate circuits from damage and electromagnetic interference (EMI). It also protects surrounding devices, such as TVs, from the PC's EMI.
NOTE
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 from escaping into the surrounding area. Running a computer without its cover is a sure way to generate EMI.
The case design is also often used to underscore the identity of a specific brand of computer, and can often be part of the reason we purchase a particular computer. Some people will also choose a case design for its appearance. We do, after all, want something that looks good, especially if we are spending a lot of money on it. With some cases, however, there may be a more technical reason for the case choice, such as the number of drive bays available.
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.
As computer technicians, we don't usually concern ourselves with the computer case; we simply deal with whatever our customer uses. 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 can be important.
When considering the case, there are four general rules to keep in mind:
- The bigger the box, the more components it can hold (providing greater expansion potential) and, often, the better the air flow (essential for cooling). Large cases are also 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 air flow is more restricted.
- Smaller cases that come with a power supply usually have lower wattage, reducing the number of internal devices that can be installed.
- The more features in a case design, like the power wattage or the number of bays, the higher the cost.
IMPORTANT
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 air flow and reduced cooling of the system components. If you must do so, consider placing a small fan so that it blows an air stream over the CPU and chip set.
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 cover 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. However, 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.
Another trend is a case design using fittings that can be opened without any tools. Some computers now provide easy opening with a thumb screw that doesn't even require a screw driver. If you are working with one of these computers, simply turn the thumb screw and slide the case back.
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.
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