Hardware Reference
In-Depth Information
Most new circuit boards, like a replacement video card or sound card, come in an
antistatic plastic bag. These bags have a coating that collects static charge on the outside of
the bag, keeping it away from what's inside the bag. Expensive circuit boards should always
be stored in an antistatic bag when not in use. Computer stores sell extra bags, but most
people accumulate a collection of them simply from buying and installing new hardware.
Finally, you can buy antistatic spray that minimizes static charge in your environment.
This is usually a colorless, odorless liquid in a pump bottle that you spray on the carpet and
on your clothing.
Electromagnetic Interference
Electromagnetic interference (EMI) is caused when electricity passing nearby generates
a magnetic fi eld that interferes with the operation of a cable or device. Another name for
this is crosstalk . It occurs only when the PC is on, and it goes away when the PC is off.
It causes no permanent damage (usually), but can cause data loss if the affected cable is
transporting data.
The Strata objectives include the acronym EMP, which stands for
electromagnetic pulse, in the Acronyms list. The most common usage of this
term pertains to electromagnetic interference caused by nuclear blasts, which
doesn't have much to do with computers. Make sure you know what EMP
stands for, but you shouldn't need to know much more about it than that.
EMI can come from unshielded cables, high-voltage power lines, radio transmitters, or
other sources. Electricity passing through a wire generates a magnetic fi eld, and magnetic
fi elds generate electricity. Most computer cables move data via electrical pulses, so a
changing magnetic fi eld builds up around the cable. When one cable runs next to another,
each cable's changing magnetic fi eld can interfere with the data being sent along the
other cable. Why? Because changing magnetic fi elds generate electricity, and the pattern
of electricity through the cable is what forms the data being sent. When that pattern is
altered, the data can become corrupted.
EMI may be a problem when a data cable isn't carrying its data reliably to its
destination. For example, perhaps a printer is printing garbage characters interspersed
with the normal characters, or perhaps a network connection keeps timing out due to
transmission errors. Power cables can also be susceptible to EMI; this can manifest itself as
a power fl uctuation. Power fl uctuations, in turn, can cause lasting damage to equipment, so
in that sense EMI is capable of causing permanent damage.
One way to avoid EMI problems from unshielded cables is simply not to run any cables
next to one another, and not to allow a cable to be placed near any other cable. This isn't
often practical, though, because most computer users have a tangle of cables behind their
PCs going in many directions. The best thing you can do is to troubleshoot EMI problems
as they occur by selectively moving cables that are causing problems.
Another way to minimize EMI is to select the proper cables to begin with. Shorter
cables are less prone to EMI than longer ones, so use the shortest cable that will do the job.
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