computer case, case form factors, I/O shields, case components, type
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Computer case: case form factors, I/O shields, case components, type

A computer's case is more than a box which includes the drive cage, the internal compartment that holds disk drives, and almost always the power supply, among other features, all of which we discuss in this chapter. Cases come in various types called form factors, which differ in layout of components. The case's form factor needs to match that of the motherboard and the power supply. Just as with motherboards, some cases are proprietary and require proprietary power supplies and motherboards.

Cases come with various components, most of which are self-explanatory. Drive bays are areas in the front for installation of removable media (CD, DVD, floppy, Zip, etc.). The 5 1/4-inch bays are for all but the floppy drives. Cases usually come with small speakers, which are there to provide very basic sounds to the user. About all these speakers play are warning beeps and the sound of a modem connecting. These speakers are very important, because multimedia speakers don't work before Windows has booted, if Windows is in Safe Mode, or if there is a problem with the sound card.

You should know some motherboards have extremely small speakers soldered onto the board. These are little black plastic cylinders with a hole at the top. These boards don't use case speakers.

While many older PCs had key locks, few newer ones do. Locking a computer prevents it from being powered on. The most important indicator lights are the ones that show that power is on and that the main hard drive is active. The hard drive indicator is helpful to show if the hard drive is running too much (churning), or if the computer is locked up (the light does not go on even though the computer is running). On recent cases, the only button is the power button. Older cases might have a Reset button, which simply turns power off and on, and a "Turbo" button. Leave the Turbo button in the On position unless a tech support technician tells you to turn it off.

I/O shields are the metal plates that surround the ports that are built into the motherboard. They are used to shield these ports from radio frequency interference (RFI) and to provide openings in the case in the correct size and configuration for the motherboard's built-in ports.

A good quality case can have a big impact on the performance and durability of the computer. Cases sold have to meet requirements for shielding against both external RFI and interference to external devices that is generated by the computer. Good cases are designed to provide for proper airflow to keep the components from overheating. Well made cases do not have a thin tinny feel or sound when you tap on them. They have rolled edges to prevent injury. Panels should fit together well without requiring excessive effort. When the computer is running, a good case does not make excessive vibration noises. Other attributes of good cases include ease in opening and ease in accessing internal components.

Cases come in many form factors, the most common being AT, ATX, and Micro ATX. Available styles include mid-tower, small footprint, desktop (horizontal), and those cases integrated with a monitor.

Cases also vary in the difficulty of opening and accessing internal components. While most cases open easily after removing screws from the back, you will undoubtedly come across cases whose method of opening is not the least bit apparent. Some require removal of the plastic faceplate to access screws behind it, and others are so unusual that you could look at the case for an hour and not figure out how to open it. A few manuals tell you how to open the case, but the problem with that is that in many difficult-to-open cases, the manufacturer is unidentifiable.

One common style of case requires you to remove the left-side panel only as you are looking at the front of the computer, while many other styles combine the left, right, and top panels into one piece.

Once you have opened the case, you might be stumped about how to access blocked parts, particularly the processor and disk drives. Some cases are extraordinarily difficult in this respect. These often require you to remove the drive cage. Sometimes you have to disassemble the case, while others, even ones the same size on the outside, need only to be opened in order to reach all the components. In a majority of cases, all you have to do is remove the left panel. However, you might find some cases that require you to remove both the left and right panels to access the screws holding the drive cage, while others allow the drive cage to be easily removed or swung out without removing any screws. Once you remove the drive cage, if necessary, all parts should be accessible.

If you decide to replace a case, simply match the form factor to the motherboard and make sure it has the needed number of internal and external drive bays, physical size, power supply capacity (in watts), and front-panel ports. In addition, check the processor and motherboard documentation. There very well might be further limitations on the type of case that can be used.

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