The first generation of personal computers were all true desktop systems because they were built into horizontal cases made to sit on a table or desk with the widest surface next to the tabletop. But it didn't take long for somebody to turn the case up onto one side and create a tower case with a much smaller footprint.

Instead of placing the computer case on the table with the video monitor sitting on top, many users moved their tower cases down onto the floor or to remote corners of their desks.

The choice of a desktop or tower case makes no difference to the computer's performance, but it could be a very big deal to some users. Many name-brand computer makers build all their systems in tower cases, but a screwdriver shop can probably accept your order for either type.

Note In addition to desktop and tower cases, you might also find some other designs for special uses. For example, a computer for a child's bedroom might have pastel-colored plastic trim and an extra-durable keyboard and mouse. A computer for use in an engineering lab or a broadcast studio might have a 19-inch-wide front panel for mounting in a standard equipment rack.

Tower cases come in three basic sizes: full towers, typically about 2 feet tall; midsize towers, around 20 inches tall; and mini towers, about 15 to 16 inches high. As the case gets taller, there's more space inside and on the front panel for additional hard drives and other storage devices. You should choose a full- or mid-size tower if you expect to install several extra drives in your computer.

Some cases are heavier and built more solidly than others, but it's easy to find good examples of both shapes. However, many computer makers use inexpensive cases instead of increasing the prices of their finished products or cutting into their profit margins.

If you don't expect to open up the case, you might never notice the difference between an inexpensive case and one that has more features and a better design.

Besides the choice between a desktop and a tower, other things to consider when you choose a computer case include:

• Air flow: A good case should have an exhaust fan near the back wall and vent holes in the front or sides. Air should move across the motherboard and the expansion cards to move heat away from the processor chip.
• Noise control: Some cases are designed to reduce the amount of noise and vibration that the computer produces.
• Number of internal and external drive bays: Internal drive bays provide mounting space for additional hard drives. External bays offer space for devices that must be physically accessible to a user, such as a CD or DVD drive.
• Style and appearance: Does the case fit into the décor or style of the room in which it is needed?
• Color and finish: A case might be painted with a flat or a glossy finish, black, beige or a bright color, or even unpainted metal.
• Weight: Aluminum cases are lighter and more portable than similar steel cases.
• Ease of access: Some cases include removable trays and sliding platforms for the motherboard and internal drives. These features make the computer easier to assemble and repair, but they make no difference to the day-to-day user.
• Position of the controls and indicators: The power and reset buttons, the pilot light, and the disk activity light are all normally located on the computer's front panel, but the exact position depends on the case design. Some users might prefer one layout over another.
• Power supply: If you're buying a separate case to assemble your own computer from parts, the power supply might be either be included with the case or sold separately. If it's included, is the power supply rated for enough watts to support all the internal parts without overloading?