Archived from groups: microsoft.public.windowsxp.newusers (
More info?)
"Bobby Jones" <BobbyJones@discussions.microsoft.com>
wrote in news:1D0D8717-0467-4C69-90E7-A226C589919B@microsoft.com:
> I have an eMachine using Windows XP and I just noticed there's a
> warning in the back of the instruction book about changing the
> battery - but there's no other mention of it anywhere.
>
> Does this desktop PC have a battery?
> What's it for?
> What happens if it runs out?
> Where can I find more info? (eMachines support seems to have a
> problem.)
>
> Thank you. As you can tell, I'm a really new user.
Your BIOS is recorded in EEPROM (electrically erasable programmable
read-only memory). It will remember its values even if all power is
removed from it. CMOS (complimentary metal-oxide semiconductor) must
remained energized to retain the values stored in it. When you boot,
the BIOS stored in CMOS gets used (unless it is corrupted which forces a
reload of values from the EEPROM into the CMOS). The battery is used to
keep the CMOS energized. It can be a fixed (i.e., soldered) black box
on your motherboard (in old PCs), a wafer battery about the size of a
nickel in a snap-in holder on the motherboard, or a small square box
with leads going to your motherboard (usually a replacement battery for
soldered-on batteries that went dead).
The lithium wafer batteries have a shelf life 5 years. Due to
manufacturing storage, shipping, more storage at the builder, storage
for the computer it is in, and other delays before you actually get the
computer with that battery, the battery could already be a year or two
old. So replace them at 3-year intervals, or whenever you notice your
system clock is getting off (presuming you don't run a time-sync program
to connect out to a server to continually resync your clock which can
mask the time sync problem with a low battery), or when your BIOS
settings keep reverting back to their EEPROM defaults (because the CMOS
gets no juice to keep it alive).
http://www.computerhope.com/help/cmos.htm
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