Your Computer Can't Keep Time
A computer needs a certain amount of information to operate; for example, the date
and time, the amount of memory installed, the number of drives and their configuration,
and so on. In the early days of computers, either the user typed in this information
each time the computer started, or it was set using DIP switches and jumpers. Today,
computers store this information in a CMOS chip that uses a small battery to retain
the information when the computer is shut off.
CMOS (complementary metal oxide semiconductor) is type of chip that consumes very
little power; therefore, while the computer is turned off, the battery discharges very
slowly. But the battery will totally discharge if you leave your computer turned off
for a year or so. Even if you turn your computer on every day, the battery is designed
to last only a couple of years. Occasionally a battery will fail prematurely.
Today's plug-and-play computers can detect most of the necessary settings, but if your
CMOS battery is dead, your computer will not be able to retain the date and time. The
computer will also lose any custom settings, for example, the boot sequence. If you set
a password in CMOS, you may be locked out of the computer. If the CMOS battery does fail,
you might receive the message "System Configuration Lost" when you start the computer.
It would be wise to record all the CMOS settings as a precaution.
To record the CMOS settings, watch for an on-screen prompt when you first start your
computer. The prompt tells you to press a key, usually the Del or F2, to enter CMOS.
To enter the CMOS configuration utility, you have to press the indicated key while the
message is on the screen. After the CMOS configuration screen appears, follow the
instructions provided to page through all the screens and record all the settings.
If your computer loses its time setting overnight, the CMOS battery may not be holding
a charge. The CMOS battery is located inside the case on the motherboard. Changing the
battery is usually a job for a computer technician. In fact, a layman might not even be
able to find the battery.
If you want to locate the CMOS battery in your computer, be aware that a static
discharge from your hands can damage components inside the case. After taking proper
precautions, open the case and look on the motherboard for a battery. If you have a
diagram of your motherboard, locate the battery on the diagram first.
Different motherboards use different types of batteries. The battery may be shaped
like a barrel or a coin. Some motherboards use a component that resembles a chip which
contains the CMOS and the battery (made by DALLAS or Benchmarq). Batteries come in
different voltages, so make sure you get an exact replacement.
Sometimes the battery is mounted in a holder. Sometimes it is soldered to the motherboard.
De-soldering and re-soldering a battery is usually a job for a computer technician.
An inexperienced solderer can cause a lot of damage. If you want to try to do it yourself,
first practice on an obsolete circuit board. You may change your mind.
If the CMOS battery has failed because it's too old, this might be an opportunity to
upgrade your motherboard. When upgrading a motherboard, the most important considerations
are to make sure the new motherboard is the correct form factor for your case, and that
the new motherboard has the correct bus connector slots for your expansion boards.