What causes my computer's clock to lose time?

Posted By : Ken Colburn of Data Doctors on December 11, 2000


My computer’s clock loses time on an irregular basis. It isn’t consistent but it is irritating! What is the problem and what can I do?



This question was answered on December 11, 2000. Much of the information contained herein may have changed since posting.

Personal computers can accurately calculate huge equations, track our personal finances to the penny and find a single word amongst a thousand sentences in a few seconds, but they can’t keep time! Personal computer time keeping systems are notoriously inaccurate and can experience errors as large as 5 minutes per day An error rate of 5 minutes per day is about 3500 parts per million As a comparison, a quality wrist watch will have an error rate of approximately 5 seconds per week or 25 parts per million.

Personal computers incorporate not one but two clocks to keep time and still can’t get it right The first one is often referred to as the RTC (Real Time Clock) and the second one is usually referred to as the “system clock” which is controlled by the OS (Operating System) The RTC is a piece of hardware that has its own battery and its only purpose is to keep time when the computer is turned off and give the “system clock” the time when the computer is turned on The system clock then keeps time while the computer is running

These two clocks actually run independent of one another and are only synchronized when the system is started Depending upon your symptoms, it may be a hardware (RTC) or a software (OS) problem that is causing your situation.

If your system loses time while it is turned on but regains the proper time when you restart your computer, the hardware (RTC) is working properly but your software (OS) is not able to keep time In many computers, the operating system is likely being thrown off by applications or third party utilities, such as screen savers, utilities or anti-virus programs To test for third party interference, simply restart your computer in Safe Mode (hold the Shift key down during startup) and let it run for the normal period of time that it would normally lose time If it keeps time, one of the programs that you are running in the background of the system is causing the problem

If your system is not keeping time when it is turned off, it may be the internal battery Most computers use coin shaped lithium/manganese-dioxide batteries that should be replaced every 3-4 years.

Or, it could be that your computer’s clock(s) are just plain inaccurate If you really want your clock to behave, you can use the Internet to synchronize your clock to an atomic clock! A free utility from AnalogX called Atomic TimeSync will contact the National Institute of Standards and Technology website and synchronize your system clock to their cesium atomic clocks This utility can be configured to automatically synchronize your clock at desired intervals and can even be used to synchronize all the computers on a local network You can download a copy at <a href="http://www.analogx.com/contents/download/network/ats.htm"><font color="#003399">>http://www.analogx.com/contents/download/network/ats.htm</b></font></a>

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Posted by Ken Colburn of Data Doctors on December 11, 2000


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