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#1
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Clock accuracy
Is the source of the clock time in the task bar in XP Home accurate? Like
WWV maybe? TIA -- "Where there's smoke there's toast!" Anon |
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#2
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Clock accuracy
On 05/26/2013 10:44 AM, KenK wrote:
Is the source of the clock time in the task bar in XP Home accurate? Like WWV maybe? TIA If you have it set to synchronize with a time server, then yes. Otherwise the time is simply kept by your BIOS clock and will drift slightly. http://www.microsoft.com/resources/d....mspx?mfr=true -- https://www.createspace.com/3707686 |
#3
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Clock accuracy
philo* wrote in :
On 05/26/2013 10:44 AM, KenK wrote: Is the source of the clock time in the task bar in XP Home accurate? Like WWV maybe? TIA If you have it set to synchronize with a time server, then yes. time.nist.gov ok? Otherwise the time is simply kept by your BIOS clock and will drift slightly. http://www.microsoft.com/resources/d...xp/all/proddoc s/en-us/windows_date_it_overview.mspx?mfr=true -- "Where there's smoke there's toast!" Anon |
#4
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Clock accuracy
KenK wrote:
philo wrote in : On 05/26/2013 10:44 AM, KenK wrote: Is the source of the clock time in the task bar in XP Home accurate? Like WWV maybe? TIA If you have it set to synchronize with a time server, then yes. time.nist.gov ok? Yes. The US Government keeps reasonably accurate time. |
#5
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Clock accuracy
From: "KenK"
philo wrote in : On 05/26/2013 10:44 AM, KenK wrote: Is the source of the clock time in the task bar in XP Home accurate? Like WWV maybe? TIA If you have it set to synchronize with a time server, then yes. time.nist.gov ok? Otherwise the time is simply kept by your BIOS clock and will drift slightly. http://www.microsoft.com/resources/d...xp/all/proddoc s/en-us/windows_date_it_overview.mspx?mfr=true http://www.nist.gov/pml/div688/grp40/its.cfm http://tf.nist.gov/tf-cgi/servers.cgi -- Dave Multi-AV Scanning Tool - http://multi-av.thespykiller.co.uk http://www.pctipp.ch/downloads/dl/35905.asp |
#6
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Clock accuracy
KenK wrote:
Is the source of the clock time in the task bar in XP Home accurate? Like WWV maybe? TIA Well, first you check your "Date and Time" properties, and see whether you're pointed at an actual, working, time source. Mine is set to time.windows.com right now. My modem/router, points to 2.pool.ntp.org , which is a load balanced pool of hundreds of NTP time servers. By pooling resources, no one server owner is plagued with time stamping all the computers on Earth. The bandwidth used, is actually an issue for those owners. The more servers in the pool, the less each server owner is paying as a "donation". ******* You can turn on logging, but the log file is "filled with crap". I've extracted a few lines, that gives me some idea it is running. "How to turn on debug logging in the Windows Time Service" http://support.microsoft.com/kb/816043 C:\WINDOWS\Temp\w32time.log 150608 21:35:00.7031250s - Polling peer time.windows.com 150608 21:35:00.7031250s - Sending packet to time.windows.com .... 150608 21:35:00.7812500s - LocalClockOffset: 0:00.486668500s So far, nothing stands out in that file, to suggest Windows uses a "linear dribble" correction model. A third-party NTP client, may actually have better internal modeling than the Windows one. But that's only for purists, and for people lucky enough to not have any hardware issues. (Hardware issues can swamp even the best software...) ******* Your computer has more than one clock. When the computer is off, the RTC in the Southbridge keeps time. The RTC uses a 32768Hz watch crystal, and the crystal can be located near the Southbridge. But the communications path to that hardware, is extremely poor, and so it is not practical to look up the time from that time piece on a regular basis (like, once a second). When the OS boots, RTC time is copied to a software clock service. The software clock counts "clock tick interrupts". The clock tick interrupts, in turn, are traceable to the clockgen chip and the crystal located next to it. So the "drift" of your system, is determined by more than one crystal. While the clockgen also contributes a reference clock to the CPU itself (for the CPU PLL), we don't even want to discuss how that works (SpeedStep, ugh!). Counting clock tick interrupts, avoids worrying about whether the CPU is running 2GHz or 3GHz right now. There are actually other time pieces inside the computer, beside counting clock ticks, and they all have to be synchronized, somehow. A good NTP implementation, uses linear drift compensation. Meaning, if the RTC or Clockgen loses 50ppm per day, the software clock can "dribble out" small corrections to the clock, on a more frequent basis. But linear modeling doesn't even come close to real-world behavior. (Drift could be temperature sensitive, room temp changes...) If clock tick interrupts ever get lost, due to some high priority activity taking longer than a clock tick, then the clock will randomly drift in one direction. NTP cannot really compensate for that, very readily. You can never turn up the NTP correction rate high enough, to take care of every problem type. Owners of motherboards with Nforce2 chipset, they had a problem with time that was so bad, that no NTP method could keep up with the random drift. It was short term random, meaning the on-screen (analog-looking) clock, couldn't even time 60 second periods without huge errors. There was some kind of bug in the interrupt logic of the motherboard, and one trigger condition, was a non-canonical adjustment of hardware clock (like, setting your DDR333 DIMM to run at DDR320, that sort of thing). No NTP algorithm, can successfully correct for short term random +/- type events. And that clock could be off by seconds per minute, gaining one minute, losing the next. Returning hardware timing clocks to nominal (run DDR333 DIMM at DDR333 rate), would cure the problem for some, but I think there were still a few victims, where nothing worked for them. I had one of those motherboards, but didn't have a bit of trouble with mine. Go figure. ******* The best-written articles on time keeping, come from the software developers who do VM software. Check the VMWare, VirtualBox sites and the like, as they explain how PIT works, whether they use HPET, that sort of thing. And they'll give some ideas, how OSes keep time. The copying of the RTC to the software time service, is just a small part of it. Paul |
#7
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Clock accuracy
philo* wrote:
KenK wrote: Is the source of the clock time in the task bar in XP Home accurate? Like WWV maybe? If you have it set to synchronize with a time server, then yes. Otherwise the time is simply kept by your BIOS clock and will drift slightly. Only until the OS loads. Then the BIOS clock (real-time chip) is no longer used and the OS system clock is used -- which means on a heavily loaded host the OS clock does and will get off hence why Windows comes with a time sync service to get time for a NTP server. The RTC drifts very little until the CMOS battery gets low (which means the RTC doesn't get enough or no power when the host is powered down as it does get power when the computer is up). As I recall from the last time I checked, the RTC chip drifts about 1 minute per year. However, the OS clock can drift a lot on a heavily loaded (very busy) computer. If you're constantly editing or converting video files then the OS clock will drift more. The hardware clock (RTC) is very good at keeping time. The OS clock is not hence the need to re-sync it periodically. http://www.microsoft.com/resources/d....mspx?mfr=true Microsoft's own NTP servers are heavily overloaded. They didn't ramp up their capacity as more consumers purchased their Windows products. The result is that your host may not get synchronized to their NTP server for a long time, like weeks. During that time a heavily used host get off so far in time that SSL connects won't work (because the tokens passed during the handshaking are timestamped and old tokens are considered invalid in an attempt to prevent interference and enhance security). If the system clock lets you pick a different NTP server than Microsoft's then do that. Microsoft only included one other NTP server but that gov't one is also highly targeted. You can add to the list of available NTP servers from which you can select by going into the registry and adding them to: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\Curr entVersion\DateTime\Servers I have Microsoft's NTP server, a few from the gov't, and my local university's NTP server (which is the one I pick). Once you add more NTP servers to which you can more reliably connect so you actually do get a time sync (you can check the Event Logs to see how often the sync fails), you go into the OS clock setting to select that server. Remember that the Windows Time Service will only sync your OS clock about once a week no matter which NTP server you pick. If you want more frequent updates than that, like you are operating a file server where timestamps are critical, then you need to employ 3rd party NTP software. 3rd party time sync utilities often have a long list of available NTP servers and some of them will measure the time delay from each to give you the one with the least lag which may not always be the same NTP server nor even the most physically close NTP server (because nodes in the route can vary in their delay in routing traffic). There are lots of free "atomic clock" time sync utilities out there. Some are very basic and do nothing more than the Windows Time Service other than sometimes provide you with a pre-compiled list of NTP servers so you don't have to go find them with an online search. The simple ones let you pick an NTP server but never change to another one. Some are better in that they test the NTP servers to determine which is the best one for you to use at the time for the sync and will move onto another one if the sync fails (no connect, server won't respond, host not reachable, timeouts). I use Socke****ch (payware) but it's pretty old. NTP hasn't changed but the pre-compiled list that comes with Socke****ch is out of date and you have to manually edit its text database file after figuring out its syntax. There are others that are probably as good but I haven't bothered to investigate them. After getting away from the 2 NTP servers pre-defined in Windows (Microsoft's and the common NIST one), I don't run into failed sync attempts when using my university's NTP server. Once per week (providing you really do get one every week) is enough for my host. However, if I was using it far more heavily and constantly doing so then I'd go back to use 3rd party NTP software. An offset of a minute per week (usually it's under a few seconds) for how I do load my OS is small enough for me not to worry. While the Windows Time Service adds entries into the Event Log (system) each time it attempts a sync event, it won't tell how off was the offset that had to be compensated. 3rd party NTP software might but you'll have to check their UI to see if they report how much was the change they made to the OS clock. |
#8
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Clock accuracy
Besides the registry key mentioned for where you can add (or remove)
NTP servers (so you could have one, or more, from which to select that are more reliable for connects), there are other registry settings to configure the Windows Time Service (W32time) if you intend to stick with what came with Windows instead of using a 3rd party NTP sync tool. See: http://technet.microsoft.com/en-us/l...(v=ws.10).aspx Lots of settings there and many you (and I) really can't decipher as to what they do. Of interest is the description for: Key: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Servic es\W32Time\TimeProviders\NtpClient Data item: SpecialPollInterval This is where you can specify how many seconds between poll intervals. The defaults a 604800 seconds (1 week) for most Windows hosts, 3600 seconds (1 hour) for Windows hosts logged into a domain server. You could reduce this to 86400 seconds (1 day) to *try* to get Windows to sync once per day. I said "try" because with this value my Windows host often syncs every 3 days, not every day. So it seems this is more of an eligibility setting for how long after the prior update when might be the next one rather than the actual next scheduled update interval. I had this changed to 86400 seconds (1 day) for quite awhile now. The 3 days that I typically get for the actual poll interval is usually often enough to catch just a few seconds of OS clock drift on my host for how I currently use it. If my host were far more heavily loaded then I'd probably reduce this eligibility polling interval to a lower value. Note that if you poll too often the NTP server may consider this abuse and they decide to block your IP address for awhile. |
#9
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Clock accuracy
Frank Williams schreef:
On 26 May 2013 15:44:24 GMT, KenK wrote: Is the source of the clock time in the task bar in XP Home accurate? Like WWV maybe? TIA No just install Atomic Clock http://www.worldtimeserver.com/atomic-clock/ I like TimeSync, it's very small, only 46 kb, no need to install. http://www.horstmuc.de/wrem.htm#timesync Zanqeutil |
#10
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Clock accuracy
KenK expressed precisely :
Is the source of the clock time in the task bar in XP Home accurate? Like WWV maybe? TIA smallest I know of, Neutron V1.07, only 13.9 kb unzipped. http://www.portablefreeware.com/index.php?id=320 -- Zo "Experience is what you get when you were expecting something else." |
#11
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Clock accuracy
In message , Zo
writes: KenK expressed precisely : Is the source of the clock time in the task bar in XP Home accurate? Like WWV maybe? No, it's based on the clock on your motherboard. There are plenty of utilities that _will_ synchronise you to one of a reasonably large list of "time servers" around the world (I don't know if including WWV), such as that below, but remember that none of these give you accuracy better than the cross-internet propagation time: they basically send a "what time is it" query to whichever time server you choose (or is hard-coded into them), and amend your clock based on the reply. You don't know how long the query took to work its way over the internet to the server, nor how long it took for the reply to get back to you, so it's not _that_ accurate. Some of the utilities won't amend your clock by more than a certain amount (sometimes user-settable) to avoid problems due to a really bad exchange of request/reply. If all you want to do is to guard against your clock having been accidentally set wrongly (or if it has a bad drift - though that's usually a sign the CMOS cell needs replacing), they're fine. TIA smallest I know of, Neutron V1.07, only 13.9 kb unzipped. http://www.portablefreeware.com/index.php?id=320 -- J. P. Gilliver. UMRA: 1960/1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf When I'm good, I'm very good. But when I'm bad - I'm better! (Mae West) |
#12
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Clock accuracy
On 5/26/2013 3:35 PM, VanguardLH wrote:
philo wrote: KenK wrote: Is the source of the clock time in the task bar in XP Home accurate? Like WWV maybe? If you have it set to synchronize with a time server, then yes. Otherwise the time is simply kept by your BIOS clock and will drift slightly. Only until the OS loads. Then the BIOS clock (real-time chip) is no longer used and the OS system clock is used -- which means on a heavily loaded host the OS clock does and will get off hence why Windows comes with a time sync service to get time for a NTP server. The RTC drifts very little until the CMOS battery gets low (which means the RTC doesn't get enough or no power when the host is powered down as it does get power when the computer is up). As I recall from the last time I checked, the RTC chip drifts about 1 minute per year. However, the OS clock can drift a lot on a heavily loaded (very busy) computer. If you're constantly editing or converting video files then the OS clock will drift more. The hardware clock (RTC) is very good at keeping time. The OS clock is not hence the need to re-sync it periodically. Whoa! Where on Earth did you hear that? Manufactures don't spend much money on computer clocks and I hear they spend only a buck or two on this in hardware. And IMHO they keep time as well as your average $10 watch. And during one month, I would expect the worst to lose a minute or more per month. I normally use an old program called Dimension 4 v5 which stores all of the information about time and checks it with a server that uses atomic time (you can still download it). And if I haven't used that computer in a year or two, 10 minutes or more being off isn't uncommon. -- Bill Dell Latitude Slate Tablet 128GB SSD ('12 era) - Thunderbird v12 Intel Atom Z670 1.5GHz - 2GB RAM - Windows 8 Pro |
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