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#11
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Why aren't computer clocks as accurate as cheap quartz watches?
Most older motherboards used the Dallas real-time clock chip, which had
a cheapo oscillator built in, and could use an external crystal for precision timekeeping. A good crystal will add a couple of dollars to the price of the motherboard, but the clock ic itself was over ten bucks. I use these chips in some other pieces of equipment and they are very accurate when given a good crystal for a timebase. I don't know what they put on modern motherboards. I throw computers out when they stop working now. However, the datasheet for the Dallas chip gives some hints that may be useful here. If the chip is put in an electrically noisy device like a computer, it can be accelerated by stray signals picked up by the clock circuit. I believe that NTP machines (usually) set the RTC on shutdown, as the cpu is more likely to be on time if it's been syncing itself with an atomic standard. |
#12
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Why aren't computer clocks as accurate as cheap quartz watches?
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#13
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Why aren't computer clocks as accurate as cheap quartz watches?
Watches have an internal capacitor to adjust for each
crystal. I have never seen that capacitor on motherboards since (I believe it was) the IBM AT. Furthermore, the PC clock operates at two significantly different voltages that will change crystal frequency. Battery voltage and voltage when PC is powered will cause additional fluctuation. Which voltage should they adjust the capacitor to? Just easier to not install and adjust the capacitor. wrote: I'm looking for a techical explanation. |
#14
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Why aren't computer clocks as accurate as cheap quartz watches?
On Wed, 26 Oct 2005 17:46:28 -0500 jakdedert
wrote: wrote: Why do the battery powered clocks in personal computers tend to keep worse time than quartz watches, even the $1 ones? I've often wondered the same thing...also why a $9 alarm clock will have provision for battery backup, but $200 VCR (back when VCRs were $200) needed to be rweset with each blip in the mains voltage. I recently discovered that early Sony Beta VCRs (at least) actually had back-up NiCad batteries which would keep the clock going for seveeral minutes of blackout. I just replaced one today, with a NiMH, and will replace a couple more in the next few days. I'm sure I knew about these at one time, but I just forgot about them until other things got me lnside that VCR again. - ----------------------------------------------- Jim Adney Madison, WI 53711 USA ----------------------------------------------- |
#16
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Why aren't computer clocks as accurate as cheap quartz watches?
Well I can't answer your question but for those who don't know, XP has
an automtic time synchronization feature which operates weekly. You have to be on line of course. The synchronization can also be done manually. See: StartControl PanelDate and Time. My pc keeps time very well. Glenn On 26 Oct 2005 15:03:04 -0700, wrote: Why do the battery powered clocks in personal computers tend to keep worse time than quartz watches, even the $1 ones? The computer batteries measure fine, at least 3.15V. I thought that the problem was temperature swings in the computers (25-38C), but a couple of cheapo watches taped inside the computers kept better time. |
#17
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Why aren't computer clocks as accurate as cheap quartz watches?
On Wed, 26 Oct 2005 23:25:49 GMT, Don Bruder wrote:
Dunno if it's still true in PC-land - I've been living in a Mac world for a LONG time now - but when I was playing with them years ago, the I've always wondered why the batteries in macs run down so quickly. I rarely see a PC newer than 10 years old with a bad battery, but I consistently see 3-5 year old macs with totally dead clock batteries. Macs even have a much larger (and more expensive) lithium cell than most PCs. I've seen a few 15 year old 486's with the same type and brand battery used by apple that still measures full voltage. I think the answer to the original question is just no quality control for clock accuracy. My current PC is pretty accurate, but it's still not as good a cheap watch. Andy Cuffe -- Use this address until 12/31/2005 -- Use this address after 12/31/2005 |
#18
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Why aren't computer clocks as accurate as cheap quartz watches?
In message Jim Adney
wrote: On 26 Oct 2005 15:03:04 -0700 wrote: Why do the battery powered clocks in personal computers tend to keep worse time than quartz watches, even the $1 ones? There are 2 causes. The first cause is that the internal clock (real time clock) on the motherboard is a device which the motherboard manufacturer much buy from someone else. They can buy this item in various degrees of precision, but the cost goes up as you request more precision. Since there is lots of pressure to keep cost down, but not so much pressure to keep good time, the motherboard manufacturers don't press for highly accurate real time clocks. And at the end of the day, most users have internet access these days, so it's less critical since the clock will be updated by most modern operating systems automatically. The second reason was explained by someone else. It's the fact that the OS clock can fall behind the real time clock due to the way the OS is written. This error is minimal when your computer is first booted up, but it can become significant if it is left running for days. This error is reset to zero each time you reboot. It's worth noting that an OS can correct for this too, either by using an external time source when available, or periodically resynchronizing from the BIOS clock if no reliable external source is available. -- Is it my imagination, or do buffalo wings taste like chicken? |
#19
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Why aren't computer clocks as accurate as cheap quartz watches?
On Wed, 26 Oct 2005 23:25:49 GMT, Don Bruder put
finger to keyboard and composed: In article . com, wrote: Why do the battery powered clocks in personal computers tend to keep worse time than quartz watches, even the $1 ones? The computer batteries measure fine, at least 3.15V. I thought that the problem was temperature swings in the computers (25-38C), but a couple of cheapo watches taped inside the computers kept better time. Dunno if it's still true in PC-land - I've been living in a Mac world for a LONG time now - but when I was playing with them years ago, the battery-backed real-time clock was read once at startup to set the computer's software clock, which then kept time by counting clock interrupts generated by the motherboard timing circuitry. It's true for Win98, but I don't know about XP. Just for fun, here's something interesting that I discovered recently: http://groups.google.com/group/comp....e=source&hl=en I could make time run backwards on a Win98SE machine by doing something innocuous. -- Franc Zabkar Please remove one 'i' from my address when replying by email. |
#20
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Why aren't computer clocks as accurate as cheap quartz watches?
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