This may sound a bit less relevant but I couldn't think of a better place to ask this question.

Now consider this situation, you install an OS on your system, set the timezone and time, do some stuff and turn it off. (Note that there is no power going in to the computer).

Now next time (say after some hours or days) you turn it on again, and you see the updated time.

How is this possible even when my computer is not connected to the internet and was consuming no power during the period it was down.(Is there some kind of hardware hack?)

please clarify!

  • 2
    Batteries are included.
    – nb2580
    Apr 2, 2010 at 11:08

3 Answers 3


CMOS Battery

  • 1
    Though I would appreciate some more info on what that battery powers ;-)
    – Ivo Flipse
    Apr 2, 2010 at 11:22
  • Typically the battery powers only two things, the clock and the CMOS. That's the reason your BIOS settings remain intact when the computer is powered off. Otherwise you would have to reconfigure your BIOS settings every time you boot your computer.
    – BBlake
    Apr 2, 2010 at 12:06

there is a battery on mother board, so there is always a power source. try to remove it if you have spare computer :) clock is piece of hardware that is powered by that battery.


Systems can also obtain or adjust the time from a network time server, using protocols NTP (Network Time Protocol) or SNTP (Simple Network Time Protocol). Many operating systems are configured to do this automatically.

This is more to adjust the accuracy of the CMOS clock, which is still the primary timekeeper on the local machine.

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