# Computer Clock Question **URL:** \ **Category:** Factual Questions\ **Created:** [August 24, 2002, 9:44pm UTC](https://boards.straightdope.com/t/computer-clock-question/125409 "2002-08-24T21:44:29Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![interface2x](https://avatars.discourse-cdn.com/v4/letter/i/c0e974/32.png) [@interface2x](https://boards.straightdope.com/u/interface2x)\ **Post date:** [August 24, 2002, 9:44pm UTC](https://boards.straightdope.com/t/computer-clock-question/125409/1 "2002-08-24T21:44:29Z")
I have a question relating to the time clock on computers - why is it that every computer I’ve ever had has a slow clock? It seems that every computer that I’ve ever had at home (my work one seems fine, which may be because it’s on a network) has a clock that will fall behind by about 5-6 minutes after a couple of months. Do you think this might have to do with the fact that I’m running it off of the same processor that I’m running programs, so the clock program might get slowed down slightly just the same as a normal program? That’s my only posssible explanation. Otherwise, ya got me. Any ideas? ---
**Author:** ![Ringo](https://avatars.discourse-cdn.com/v4/letter/r/779978/32.png) [@Ringo](https://boards.straightdope.com/u/Ringo)\ **Post date:** [August 24, 2002, 9:51pm UTC](https://boards.straightdope.com/t/computer-clock-question/125409/2 "2002-08-24T21:51:37Z")
I don’t know why they do, but all PC clocks seem to run slow. The one I use at work loses ~7 minutes/day. [NISTime](http://www.parkenet.com/apl/NISTime.htm) is a program you can download that will sync your PC clock with a signal from the National Institute of Standards and Technology (NIST) Internet Time Service. ---
**Author:** ![Duck\_Duck\_Goose](https://avatars.discourse-cdn.com/v4/letter/d/50afbb/32.png) [@Duck\_Duck\_Goose](https://boards.straightdope.com/u/Duck_Duck_Goose)\ **Post date:** [August 24, 2002, 9:53pm UTC](https://boards.straightdope.com/t/computer-clock-question/125409/3 "2002-08-24T21:53:20Z")
[http://www.pcnineoneone.com/howto/slowclock.html](http://www.pcnineoneone.com/howto/slowclock.html) > [@](#): > > The first step to determine whether it is just set wrong or actually lagging is to reset the clock by double-clicking on the clock and entering the correct time. I like to set it by dialing POPCORN on the phone (767-2676) and setting it to the correct time. Watch the clock for a few days and see whether it stays correct or continues to fall behind. > > \< snip \> > > If it still continues to lag, then the reason might be a dying motherboard battery. The time is stored in a little chip on the motherboard and that chip is powered by a small battery so it can hold the stored settings even if you turn your PC off. When that battery gets low, the first symptom is usually a slow clock. These batteries are made to last several years but depending on the age of your PC they will eventually die… [more] ---
**Author:** ![Swede\_Hollow](https://avatars.discourse-cdn.com/v4/letter/s/3bc359/32.png) [@Swede\_Hollow](https://boards.straightdope.com/u/Swede_Hollow)\ **Post date:** [August 24, 2002, 9:58pm UTC](https://boards.straightdope.com/t/computer-clock-question/125409/4 "2002-08-24T21:58:47Z")
It’s usually just bad quality control by the manufacturers of the clock componant. It reminds me of my first 4-head VCR years ago that gained 9 minutes per month. The VCR was “repaired” under warranty but the dealer had to go through 4 or 5 chipsets until one was within the manufacturer’s spec’s. It lost 7 minutes per month but that was within the tolerances allowed for the clock. PC clock makers are just trying to keep costs down by making “good enough” products instead of trying to invest in quality. 1 of my home PC’s loses about 5 minutes a month, the other two stay right on target. ---
**Author:** ![ftg](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ftg/32/2801_2.png) [@ftg](https://boards.straightdope.com/u/ftg)\ **Post date:** [August 24, 2002, 10:03pm UTC](https://boards.straightdope.com/t/computer-clock-question/125409/5 "2002-08-24T22:03:13Z")
While lack of quality in the components is a common problem with a slow clock and good battery, the OS and some apps. can also cause problems. Certain MS OSes with certain settings can make clocks run slow. There’s MS technotes about these problems (but I have better ways of dealing with it :)). ---
**Author:** ![handy](https://avatars.discourse-cdn.com/v4/letter/h/b5a626/32.png) [@handy](https://boards.straightdope.com/u/handy)\ **Post date:** [August 24, 2002, 10:30pm UTC](https://boards.straightdope.com/t/computer-clock-question/125409/6 "2002-08-24T22:30:48Z")
interface2x, how did you check the time? At the Dos prompt, Bios or in your operating system? They are not done the same way, so which way are you using & what OS & is it a PC or a Mac? ---
**Author:** ![scotth](https://avatars.discourse-cdn.com/v4/letter/s/b9e5f3/32.png) [@scotth](https://boards.straightdope.com/u/scotth)\ **Post date:** [August 24, 2002, 11:28pm UTC](https://boards.straightdope.com/t/computer-clock-question/125409/7 "2002-08-24T23:28:52Z")
Almost all PC’s (I would say all, but then someone would find an exception) have a real time clock circuit that runs independent of the CPU, any programs, OS, etc. In fact it runs when the computer isn’t even turned on. If it is not keeping good time, this circuit is most certainly the problem. ---
**Author:** ![rowrrbazzle](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rowrrbazzle/32/414_2.png) [@rowrrbazzle](https://boards.straightdope.com/u/rowrrbazzle)\ **Post date:** [August 24, 2002, 11:50pm UTC](https://boards.straightdope.com/t/computer-clock-question/125409/8 "2002-08-24T23:50:25Z")
At one place I worked, they set up their own time server which synched to one of the public time servers. Then the work pcs could synch to the work time server. interface2x’s work pc could be set up to synch automatically to a work time server or directly to a public server. On my home pc, my clock drifts around one minute per month, and I synch it once a month. ---
**Author:** ![screech-owl](https://avatars.discourse-cdn.com/v4/letter/s/82dd89/32.png) [@screech-owl](https://boards.straightdope.com/u/screech-owl)\ **Post date:** [August 25, 2002, 12:49am UTC](https://boards.straightdope.com/t/computer-clock-question/125409/9 "2002-08-25T00:49:03Z")
> [@](#): > > \*Originally posted by Ringo \* > **I don’t know why they do, but all PC clocks seem to run slow. The one I use at work loses ~7 minutes/day…** I must have the anti-clock. Mine gains time. I noticed yesterday it is about 17 minutes faster than the cable box and the VCR, and I last reset it about a week ago. I asked about this before, but unfortunately did not get any useful answer. Darn. ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [August 25, 2002, 2:29am UTC](https://boards.straightdope.com/t/computer-clock-question/125409/10 "2002-08-25T02:29:40Z")
Computers (meaning IBM PC architecture, since the 286 days) have a real time clock chip. When the operating system starts up (dos, linux, windows) the operating system reads the current time out of the chip. From then on, while the computer is running, it updates its time based on the timer tick interrupt. So, you have two quartz crystals involved, one in the real time clock chip and one used to generate the system clock (which actually drives a bunch of different timers, including that stupid original pc speaker). When you shut down the computer, linux stores the current time back into the real time clock. Not sure about windows. DOS doesn’t. The accuracy of the clock depends on the manufacturing tolerance of the crystals. No crystal is anywhere near as accurate as an atomic clock of course, but the more accurate the crystal the more it costs, which is why PC clocks always tend to be a little off. Could be faster or slower, but it’s not likely to be exactly right.