Why aren't computer clocks as accurate as cheap quartz watches?

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.

Reply to
do_not_spam_me
Loading thread data ...

Maybe the same reason we didn't have built-in clocks until after there were five dollar LCD wristwatches. I don't know.

My current clock is very accurate (MSI ma> Why do the battery powered clocks in personal computers tend to keep

Reply to
John Doe

The short answer is that computer makers don't care.

More specifically, even cheap watches usually have a trimmer capacitor on the timebase crystal that someone actually adjusts. Computer makers usually choose to save pennies by using a fixed capacitor and not having to pay labor to adjust.

Reply to
Ol' Duffer

Supply and demand. If your watch kept bad time, you'd send it back. If your computer keeps bad time, you'll reset the clock and bitch about it on the internet. Vendors care if you send it back. They don't care if you bitch on the internet. mike

--
Wanted, Serial cable for Dell Axim X5 PDA.
Return address is VALID but some sites block emails
 Click to see the full signature
Reply to
mike

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.

FWIW, there are utilities which will update your computer clock from the National Bureau of Standards over the web.....

jak

Reply to
jakdedert

That question have been around for more than 20 years and probably longer. Even one PC magazine reported a major branded PC that used to cost $2,000 couldn't keep time as well as a $5 watch from Kmart (not exact quote but similiar to that)

The OS could check via internet at regular intrevials to make correction to the clock but that is if the PC does have internet connection at all.

--
When you hear the toilet flush, and hear the words "uh oh", it's already
too late.    - by anonymous Mother in Austin, TX
 Click to see the full signature
Reply to
Impmon

somebody wrote

Who is the manufacturer? I only use Gigabyte(mostly) or MSI (sometimes) motherboards. I find the clocks to be reasonably accurate. My guess would be that the OEM didn't ground the crystal case or use the proper guard ring techniques for noise reduction. Do you find that they run fast or slow?

Reply to
Anthony Fremont

I have one PC that will lose or gain hours at a time if the machine goes into standby, another that does ok but still drifts enough that I have to use a utility to keep it in sync with the atomic clock. On the other hand a Sun workstation that I fire up occasionally to play with keeps excellent time, even after sitting unplugged for 6 months it's usually within a few seconds but then it was originally $25K.

Reply to
James Sweet

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. That interrupt, like any other "not non-maskable" interrupt, can be blocked out for various reasons by various things, causing the software clock to lose time. Usually, the amount of "lost" time isn't really noticable except on "continuously on" machines. But with long periods between restarts, heavy use of software (or firmware... The blame may not be in your clock, but in your ROM code) that disables interrupts often or for extended periods, and/or no intervention (be it human or software) happening, it can grow to substantial amounts of time surprisingly quick.

Immediately after startup, the clock SHOULD be reasonably close to right, since it will have been freshly set from the battery powered clock, but after a while, it *WILL* go wonky unless steps are taken to correct the drift - It's just the nature of the beast.

--
Don Bruder - dakidd@sonic.net - If your "From:" address isn't on my whitelist,
or the subject of the message doesn't contain the exact text "PopperAndShadow"
 Click to see the full signature
Reply to
Don Bruder

Reply to
George

I'm looking for a techical explanation.

Reply to
do_not_spam_me

The only PC motherboards I've seen that consistently kept accurate time all had Dallas clock chips in them, and some of those chips were still running properly from their internal lithium cells (permanently encapsulated) 10 years later.

Reply to
do_not_spam_me

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.

Reply to
stickyfox

Yeah the Sun has a Dallas in it, in fact I had to hack in a new battery in one of them as the original went dead and modern chips won't work in it. Come to think of it I had a 486 PC with a Dallas, I think that was the most recent though.

Reply to
James Sweet

Reply to
w_tom

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 snipped-for-privacy@vwtype3.org Madison, WI 53711 USA

-----------------------------------------------

Reply to
Jim Adney

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.

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.

-

----------------------------------------------- Jim Adney snipped-for-privacy@vwtype3.org Madison, WI 53711 USA

-----------------------------------------------

Reply to
Jim Adney

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: Start>Control Panel>Date and Time. My pc keeps time very well.

Glenn

Reply to
gswiebeREMOVE_THIS

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

snipped-for-privacy@psu.edu

Reply to
Andy Cuffe

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.

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?
Reply to
DevilsPGD

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.