PC Hardware in a Nutshell, 3rd Edition [Electronic resources] نسخه متنی

25.2 Choosing a Case

Use
the following guidelines when choosing a case:

If you are migrating an existing motherboard, buy a case to fit that
motherboard. If you are building a new system, buy a case that
accepts full ATX motherboards, even if you're
installing a Mini-ATX or microATX motherboard. A full-ATX case allows
upgrading later to a full-ATX motherboard, and provides more working
space even if the system will never have anything larger than a
microATX motherboard installed.

Using a small motherboard (or one with poorly placed ATA connectors) in a full- or mid-tower case may require drive cables longer than the PATA maximum of 18 inches. Using ATA cables longer than 18 inches may corrupt data, particularly with Ultra-ATA hard drives. If an 18-inch cable is too short to reach a hard drive mounted in one of the top bays, you may be able to mount the drive in an internal bay that permits using the 18-inch cable. If not, consider substituting a SATA hard drive, which can use a 39-inch cable. Optical drives operate at lower data rates than Ultra-DMA hard drives, so there is less chance that data will be corrupted by a longer cable. Although we cannot recommend using P-ATA cables longer than 18 inches because they do not comply with the ATA specification, we have often used 24-inch cables for optical drives without experiencing data integrity problems.

Choose a case that leaves at least one or two baysideally
5.25-inch external baysfree for later expansion. As the price
of tape drives, DVD-ROM drives, and CD/DVD burners continues to fall,
you're likely to want to install one or more of them
in the future. That's impossible without free drive
bays. A mini/mid-tower case with three external 5.25-inchbays, two
external 3.5-inch bays, and perhaps one or two internal 3.5-inch bays
is usually the best compromise between size, cost, and available
bays, although a full tower may be the best choice if your current
configuration fills or nearly fills a mid-tower. Some cases can be
ordered with two or three optional internal 3.5-inch bays for very
little additional cost, typically $5 to $8. If in doubt, always buy
the next size up.

It's always tempting to save money, but cases are
one place where it's easy to spend too little. The
cheapest cases ($30 or $40 with power supply) are often unusable due
to misaligned holes and so on. Even midrange
"name-brand" cases often have
razor-sharp edges and burrs, which can cut you and short out wires.
Expect to pay at least $35 (without power supply) for a decent
mini/mid-tower case and $50 to $60 for a full tower. Paying 50% more
than that usually gets you a much better case.

Many cheap and midrange cases include a
"throw-away" power supply
that's of poor quality and undersized. If you have
such a case, do yourself a favor: discard the bundled power supply
and install one of the power supplies we recommend in Chapter 26. At best, cheap power supplies cause
reliability problems. At worst, we have seen cheap power supplies
fail catastrophically, taking the motherboard and other system
components with them. Better cases may be available with or without a
power supply. If the standard power supply is appropriate, you may
save a few bucks by buying the bundle. Otherwise, buy only the case
and install a high-quality power supply sized appropriately for your
needs. Standard power supplies fit standard cases interchangeably, so
compatibility is not an issue.

Heat is the
enemy of processors, memory, drives, and other system components.
Cooler components last longer and run more reliably. A processor run
at 50° C (122° F), for example, will last only
half as long as one run at 40° C (104° F), but
twice as long as one run at 60° C (140° F). The
best way to minimize temperature inside the case is to move a lot of
air through it. Although the power supply fan and processor fan may
provide adequate cooling on lightly loaded systems, adding
supplemental fans can reduce ambient case temperature by
20° C (36° F) or more on more heavily loaded
systems. Many cases can be ordered with optional supplemental fans.
If the case you order offers optional fans, order them. Otherwise,
add the fans yourself. You can purchase supplemental fans for a few
dollars from local computer stores and mail-order suppliers. They are
available in various standard sizes from 60 mm to 120 mm, so make
sure to purchase the correct size. Note that many cases that accept
multiple fans use different sizes in different locations.

Make sure supplemental fans blow the right way, including those that arrive installed in a case. Some power supplies have intake fans, and others have exhaust fans. The ATX specification recommends but does not require using an intake fan on the power supply. Many (including us) prefer power supplies that use exhaust fans, and many manufacturers now supply exhaust fans on ATX power supplies. The danger arises when the power supply fan and supplemental fan(s) blow in the same direction in a tightly sealed case. When that happens, the fans work against each other, either pressurizing the case or creating a partial vacuum. In either event, airflow is reduced or eliminated, which causes the processor and other system components to overheat. Although most cases have enough vent holes and other gaps to prevent this from becoming a problem, we still generally attempt to "balance" airflow by configuring half the fans for intake and half for exhaust. Supplemental fans can be mounted to blow in either direction. If your power supply uses an exhaust fan, configure supplemental fan(s) as intake fans. If your power supply uses an intake fan, configure supplemental fan(s) as exhaust fans. On a related issue, if your fans have foam air filters installed, check them periodically. Filters clog rapidly under dusty conditions, and a fan with a clogged filter is no better than no fan at all.

If you frequently add and remove components, consider purchasing a
case with accessibility features such as a removable motherboard tray
and drive bays. If you don't open your case from one
month to the next, you may be better served by a case with fewer
accessibility features, which is likely to be less expensive for
equivalent quality and rigidity.

When you compare case prices, remember that the cost to ship a case
can be substantial. Cases you find at local stores already have that
factored in. Mail-order companies may charge $20 to $40 to ship a
case, or even more for heavy full-tower cases.