3 ms·

"A typical laptop or server, left without any type of external time conditioning, will drift out of sync within minutes and after a few hours may already be sev

"A typical laptop or server, left without any type of external time conditioning, will drift out of sync within minutes and after a few hours may already be several minutes away from good synchronization with other systems." This doesn't match my experience at all. I've had smartphones disconnected from the network for weeks at a time without drifting "several minutes away" from the consensus time. Drift is a thing, but it seems like that estimate is several orders of magnitude larger than anything I've seen in practice.

lostcolony 11y ago
Not to mention what it'd mean about watches (the dumb kind). Digital watches as a whole, even the cheap ones I'd own as a kid, never drifted that far that fast. I can't imagine that the cheap ones had better crystals in them than a laptop. I think it may just be badly phrased. "will drift out of sync within minutes" was meant as it'll almost assuredly have gained/lost a few microseconds from what it should have, given the progression of 'real' time for its frame of reference, but that it -may- be that bad. Which, yeah, sure, it -may-. Not bloody likely, but maybe.
- YZF 11y ago
  I'm not quite sure what's in my laptop right now but it used to be that there was a separate crystal for time keeping, typically around 32KHz. I believe digital watches used similar crystals. Those drift a lot less than the high frequency crystals used to generate the CPU clock. Their accuracy is on the order of 10ppm. The other thing that matters is the temperature variation as the frequency will change with temperature. A wrist watch probably sees more uniform temperatures (esp. if it's worn all the time and e.g. has a large metallic backing). Laptops can get quite hot and quite cold. You can get temperature compensated oscillators down to about 1ppm accuracy over a larger temperature range. 1ppm is about 1 second/week. Back in the day I wrote a little utility where every time you adjusted your computer clock it took notice of the drift and fed that back into the time calculation. I.e. it continuously adjusted the clock based on the corrections given to it.
jacquesm 11y ago
For ordering purposes a few microseconds will do.
- techdragon 11y ago
  For your ordering purposes it might be, but it sure as hell is not good enough for me on a regular basis.
  - jacquesm 11y ago
    I meant that as in 'enough to get you out of wack', not the other way around. For proper ordering you'd need better than microsecond resolution so if you're off by a few microseconds you might as well use rand().

lostcolony 11y ago

Not to mention what it'd mean about watches (the dumb kind). Digital watches as a whole, even the cheap ones I'd own as a kid, never drifted that far that fast. I can't imagine that the cheap ones had better crystals in them than a laptop. I think it may just be badly phrased. "will drift out of sync within minutes" was meant as it'll almost assuredly have gained/lost a few microseconds from what it should have, given the progression of 'real' time for its frame of reference, but that it -may- be that bad. Which, yeah, sure, it -may-. Not bloody likely, but maybe.

YZF 11y ago
I'm not quite sure what's in my laptop right now but it used to be that there was a separate crystal for time keeping, typically around 32KHz. I believe digital watches used similar crystals. Those drift a lot less than the high frequency crystals used to generate the CPU clock. Their accuracy is on the order of 10ppm. The other thing that matters is the temperature variation as the frequency will change with temperature. A wrist watch probably sees more uniform temperatures (esp. if it's worn all the time and e.g. has a large metallic backing). Laptops can get quite hot and quite cold. You can get temperature compensated oscillators down to about 1ppm accuracy over a larger temperature range. 1ppm is about 1 second/week. Back in the day I wrote a little utility where every time you adjusted your computer clock it took notice of the drift and fed that back into the time calculation. I.e. it continuously adjusted the clock based on the corrections given to it.

jacquesm 11y ago

For ordering purposes a few microseconds will do.

techdragon 11y ago
For your ordering purposes it might be, but it sure as hell is not good enough for me on a regular basis.
- jacquesm 11y ago
  I meant that as in 'enough to get you out of wack', not the other way around. For proper ordering you'd need better than microsecond resolution so if you're off by a few microseconds you might as well use rand().