User guide

1-6 User’s Guide
require you to load software files called
device drivers
into system memory
before they will work.
These software drivers help the computer recognize the external device and
direct its operation.
 Dell recommends that you attach external devices
only while the computer is
turned off
unless you are instructed otherwise in the documentation for the par-
ticular device. Then turn the computer on before turning on any external devices
unless the documentation for the device specifies other wise. (If the computer
does not seem to recognize the device, try turning on the device before turning
on the computer.)
*(!+,
"-(""
)"!()
'

A number of devices are available that protect your system against power problems
such as power surges, transients, and power failures. The following subsections
describe some of these devices.

Surge protectors are available in a variety of types and usually provide a level of pro-
tection commensurate with the cost of the device. Surge protectors prevent voltage
spikes, such as those caused during an electrical storm, from entering a system
through the electrical outlet. Surge protectors, however, do not offer protection
against brownouts, which occur when the voltage drops more than 20 percent below
the normal AC line voltage level.

Line conditioners go beyond the overvoltage protection of surge protectors. Line con-
ditioners keep a system's AC power source voltage at a fairly constant level and,
therefore, can handle brownouts. Because of this added protection, line conditioners
cost more than surge protectors—up to several hundred dollars. However, these
devices cannot protect against a complete loss of power.

Uninterruptible power supply (UPS) systems offer the most complete protection
against variations in power because they use battery power to keep the system running
when AC power is lost. The battery is charged by the AC power while it is available, so
once AC power is lost, the battery can provide power to the system for a limited amount
of time—from 15 minutes to an hour or so—depending on the UPS system.