Computer cases

Computer cases (or chassis) protect the internal components of a PC from the outside environment and come in two varieties-desktop and tower. Desktop computer cases lie on a desk with the monitor sitting on top. These were the first type of PCs and there are a few that exist today. Towers stand upright. However, the term desktop is now used to describe any system that is not a laptop. Towers are the most popular and there are three types: mini, mid, and full. The front of the case is called the bezel. Each one is designed for a certain motherboard form factor. The mini case can also be a slim tower or a HTPC. HTPC stands for Home Theater PC. As the name implies, HTPC cases are specifically designed to match your audio/video system equipment.
Most lie flat like a desktop and support a micro ATX or ITX board. The mid tower and full tower support micro as well as regular ATX. When choosing tower computer cases, consider these factors:

Space - Don't have much room to spare? You may want a mini tower case. These computer cases take up very little space and can be tucked away nicely. However, at some point you may want to fix or add components to your PC. If so, then a mid or full tower case is better because they provide more space inside to work.

Number of Drive Bays - Drive bays are where you insert hard drives and CD/DVD drives. Full tower computer cases usually contain far more external and internal bays than mid or mini. Make sure you purchase a case with enough bays for present and future needs.

Number of Ports & Slots - Cases come equipped with a number of front panel audio, USB, and Firewire ports as well as slots in the back for expansion cards. Just like above, get the one that's suitable for your needs.

Number of Fans & Vents - Make sure the case has sufficient air flow. The more fans the better and many cases have additional vents on the side.

Case Material - Most cases are made of aluminum, steel, or both. Sometimes the bezel is plastic.

Power Supply - Many cases come with a power supply already installed. This can be a money saver instead of buying them separately.

Besides providing protection for parts, computer cases come in a multitude of stylish designs and colors. Many have a clear side and LED lighting so you can see inside. Remember to keep upgrading in mind. If you're thinking about adding extra drives or cards later, buy a case with plenty of space that supports those extra components.

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Refer site : learning-about-computers.com