Is It Necessary To Replace The CMOS Battery

I've never replaced mine since 1998 but was considering doing so now.
However, through power outages and moving from one town--or state--to
another, I've never lost my BIOS or CMOS settings. Why is it necessary to
really have even have one on the motherboard?
--
{ : [|]=( DaffyD®

If I knew where I was I'd be there now.

"DaffyD®" wrote in message
...
I've never replaced mine since 1998 but was considering doing so now.
However, through power outages and moving from one town--or state--to
another, I've never lost my BIOS or CMOS settings. Why is it necessary to
really have even have one on the motherboard?
--
{ : [|]=( DaffyD®

If I knew where I was I'd be there now.


It's necessary to keep the CMOS settings when there is no power current to the PC.
Try shutting down, removing the battery and rebooting if you want. Some last forever
(figuratively speaking) while others puke swiftly, you'll see definite signs when it
decides to go AWOL. AFAIK when a current is present the battery is also recharged.

--

Brian A. Sesko { MS MVP_Shell/User }
Conflicts start where information lacks.
http://basconotw.mvps.org/

Suggested posting do's/don'ts: http://www.dts-l.org/goodpost.htm
How to ask a question: http://support.microsoft.com/kb/555375

"DaffyD®" wrote in message
...
I've never replaced mine since 1998 but was considering doing so now.
However, through power outages and moving from one town--or state--to
another, I've never lost my BIOS or CMOS settings. Why is it necessary to
really have even have one on the motherboard?
--
{ : [|]=( DaffyD®

If I knew where I was I'd be there now.

Some main boards have a rechargeable battery, the majority uses a single
Lithium cell with a shelf life of 10 years. Since the ATX power supply came
into fashion, the Cmos chip is powered from the supply 24/7, so the battery
only has to deliver when there is a power outage or the PC is stored. The
battery has enough capacity to keep the clock running for 2 years. And no,
it isn't necessary anymore. Already in the 80's there were Cmos chips with
integrated power source and BIOS setup in non-volitile memory, but the
industry chose the cheapest solution.

CDK

"C.D. Koger" wrote:
Why is it necessary to really have even have one on the
motherboard?

Because when the computer is not plugged in, then something has to
power the clock.

Back before the time of the ATX power supply (when 120-volt power was
actually routed to the front power switch, which corresponds to any
286/386/486/Pentium-1 and some P-2 computers) then the battery was
always powering the clock when the computer was turned off.

The battery has enough capacity to keep the clock running for 2
years.

I think they can last longer than that. The Gigabyte 8KNXP which I
bought in late 2003 and only recently powered up had the correct date
(but naturally the time was off but I suspect it was set to Taiwan
time as most motherboards seem to be when shipped).

And no, it isn't necessary anymore. Already in the 80's there
were Cmos chips with integrated power source and BIOS setup
in non-volitile memory, but the industry chose the cheapest
solution.

What do you think was the "integrated power source" in that case?
Something other than a battery?

The industry chose the more practical solution - a 2032 3V battery
which is accessible by the user. A battery integrated inside the cmos
chip is not.

"98 Guy" wrote in message ...
"C.D. Koger" wrote:
Why is it necessary to really have even have one on the
motherboard?

Because when the computer is not plugged in, then something has to
power the clock.

Back before the time of the ATX power supply (when 120-volt power was
actually routed to the front power switch, which corresponds to any
286/386/486/Pentium-1 and some P-2 computers) then the battery was
always powering the clock when the computer was turned off.

The battery has enough capacity to keep the clock running for 2
years.

I think they can last longer than that. The Gigabyte 8KNXP which I
bought in late 2003 and only recently powered up had the correct date
(but naturally the time was off but I suspect it was set to Taiwan
time as most motherboards seem to be when shipped).

Your board doesn't have the old dip-16 Cmos clock anymore, but something far
smaller that draws less current. But after 3 years in a box, most of the
capacity has been used up by the clock and external leakage current.

And no, it isn't necessary anymore. Already in the 80's there
were Cmos chips with integrated power source and BIOS setup
in non-volitile memory, but the industry chose the cheapest
solution.

What do you think was the "integrated power source" in that case?
Something other than a battery?

Of course a lithium wet cell battery, but with enough capacity to power the
clock 10 years.
Storage has no effect, as long as 2 pins aren't tied together, the clock is
not powered. They still exist, but except on a few 486 EISA boards, I've
never seen any in PC's.

The industry chose the more practical solution - a 2032 3V battery
which is accessible by the user. A battery integrated inside the cmos
chip is not.

3 years ago, without seeing loss of cmos battery symptoms, I replaced one
oddball one. Its onboard a chip called "Dallas". Also bought a spare.
Similar age motherboard.

The cmos battery keeps alive the cmos and RTC, not the bios. The cmos holds
all your bios settings including time and date, and the PC configuration
assessed at bootup at a prior time.

There is a battery, believe me, somewhere on your motherboard.
--
Jonny
"DaffyD®" wrote in message
...
I've never replaced mine since 1998 but was considering doing so now.
However, through power outages and moving from one town--or state--to
another, I've never lost my BIOS or CMOS settings. Why is it necessary to
really have even have one on the motherboard?
--
{ : [|]=( DaffyD®

If I knew where I was I'd be there now.