how does CMOS keep the time correct?

Question

I need help, right away. I've got a project due tomorrow, and I need to know how the CMOS always has the time correct on a PC. Please help!

Answer 1

Here's your answer:
A computer actually maintains three separate clocks:

The Real Time Clock (RTC), located on the system board and powered by the CMOS battery such that it should be consistently updated even if the system is not receiving AC power.
The CMOS clock, which is a logical clock stored in the BIOS chip on the system board. Its settings are maintained (but not updated) in non-volatile RAM while the system is powered off.
The Operating System (OS) clock, which is a logical clock stored in system memory and is cleared each time the system is powered off or rebooted.
When a computer is powered on, the CMOS clock synchronizes with the RTC during the POST (Power On Self Test) operation. When the operating system boots, it reads the current time from the CMOS clock and maintains its own, essentially independent, OS clock. The OS clock does not synchronize again with the CMOS clock unless the OS clock is manually changed (at which time both the CMOS clock and RTC are set to the time stored in the OS clock), or the system is rebooted. Therefore, the OS clock may hold an incorrect time if running tasks slow down the operating system scheduler, while the CMOS clock and RTC continue to maintain the correct time.

Answer 2

After you set the time, the CMOS has the basics running on the system, like a Clock, the CMOS battery keeps the battery running
http://en.wikipedia.org/wiki/CMOS

Answer 3

The CMOS clock is an independent register on the motherboard that is more or less a counter. A small battery runs a quartz clock like that in your watch which generates pulses that the counter counts. The computer has access to this register and can convert the count in it to a date and time.

Answer 4

Do you need to create your own CMOS code?
or
Do you to use the pre-integrated CMOS code?
maybe these sites would help:
http://www.geocities.com/SiliconValley/2151/cmos.html

http://csourcesearch.net/package/dosbox/0.63/dosbox-0.63/src/hardware/cmos.cpp