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

I have seem many computers loose time, and a low battery seems to increase the loss. An online computer can also be reset. There are programs which sync to Universal Time, and networks, and even mail programs can perform syncronization automatically.

greg

Making a accurate oscillator requires two key things

1. An accurate crystal (note stability is not the same as accuracy)
2. An oscillator circuit design that does not "pull" or otherwise change the basic frequency of the crystal.

Clearly if you design a watch these are primary concerns, so even a cheap watch is done well

For a computer this not a primary concern and I am sure there is a wide range of accuracy in different models of computers depending on the amount of attention paid to these issues. My current computer with an intel mother board does keep could time.

Dan

--
Dan Hollands
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 wrote in message 
news:1130364184.236610.90350@g47g2000cwa.googlegroups.com...
> 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.
>

Right on James!

That is how the NG's are suposed to work. But you get these trolls who think there answer is the only answer. They have closed minds.

That second means nothing in itself. "IBM PC" type computers have a tiny bit of static RAM to hold the bios settings. If it wasn't there, and kept alive, you'd always have to set those things every time you turn the computer on.

Now, it may be that one uses more current than the other, but I can't really see that being a significant difference.

Michael

Just in case anybody is interested

And for the record, Tom, is relevant to the OP's question because it concerns your PC's clock keeping accurate time. It is a solution to the problem. What have you to offer?

On Wed, 26 Oct 2005 23:25:49 GMT, Don Bruder put finger to keyboard and composed:

It's true for Win98, but I don't know about XP.

Just for fun, here's something interesting that I discovered recently:

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.

So what? I had offered an answer to that as well as offering a solution. Perhaps you didn't read that part of the thread.

Now, Had I said your pc's clock will run slow because magic trolls and ferries sneak in make adjustments to the master oscillator. That might warrant an attack. But the rest of this crap is just that, crap!

you see my mind is not one dimensional, I might take a question and expound on the answer to not only give a reason why this happen but also offer a way to correct it.

And by the way, my last comment was prefaced, "Just in case anybody is interested". Obviously you are not so the post was not intended for you. In other words, Bug Off, pedal on and get a life!

Your other post is classic of those who use emotion as if emotion was logic. I will pretend you did not post an outburst in the other post; in respect for your dignity.

Below is a partial description of how the computer's other clock works. It assumes time lost will also cause the computer's battery clock to change. Do you know they both use completely different circuits and oscillators (time bases)? That battery clock does not change no matter how many seconds or days the Windows (Operating System) clock changes.

This might be true if the system is not pre-emptive multitasking or if the OS itself crashes - which is rare enough to not be relevant:

Meanwhile, as an OS gains or loses time, the computer's battery clock remains unaffected. Again, you should have known this which is why your original post used the word "might". Well, at least this time you look up some facts before posting. But you did not obtain all facts. Loss of time by the OS does not change the CMOS or battery clock. Made obvious with simple hardware or BIOS knowledge. You are advised to first learn the basic circuit - as it was designed even in the original IBM AT. The circuit is based in a famous IC - Motorola's MC146818 and an equivalent IC from Dallas Semiconductor.

Not knowing how this battery clock works is not what you are criticized for. Furthermore an emotional outburst was not posted - a lesson you should learn from. Criticism is based on facts. You posted speculation AND you posted things totally irrelevant to what the OP was asking. Not just you. This thread is chock full of posters who only speculated and who did not answer the OP's question.

Now you are also being corrected for not learning all the facts about how the battery backup data time clock works. Your "Likely culprits" list is not based on knowledge of a

1984 legacy circuit that is standard in PCs. Gain or loss of time by the OS - using a completely different clock - does not affect the battery backup clock. This true in hardware today as it was in the original IBM AT. Those "most common culprits" in no way change the date time of a battery backup clock.

What was do_not_spam_me ask> What Happens and Why

You apparently didn't read *all* the replies, but more to your question, a lot of people with too much time on their hands and too little knowledge to be useful feel compelled to type when you put a keyboard before them. Must be an ego thing...

No, I don't. Where do you see it?

UseNet is arcane and slow, so messages may take hours or even days to propagate through the system. In some cases, it is even possible to see replies before the original question. You cannot tell much about what posts someone else has seen from the time of appearance on *your* screen.

Why is speculation useless? Nobody can give one solid answer because the problem is not identical across all computers, nor is it always caused by one simple factor. I've learned a fair amount of interesting things from this thread, I guess you missed all that.

The battery backup circuit in a PC is a circuit originally in IBM AT - a legacy of that well established 1984 design using a Motorola MC146818.

To have posted as DBLEXPOSURE has, he should have first known about that circuit. A majority of posts in this thread are total speculation based upon no relevant technical knowledge. That is shameful if not irresponsible. One even claims the OS clock causes changes in a completely different oscillator - the CMOS date time clock. Again, one who did not first learn basic facts. Unfortunately too many people (often who are only programmers) somehow become experts on how hardware works. Had he even learned a PC's BIOS, then this would have been obvious.

DBLEXPOSURE demonstrates that many just know; cannot bother to first learn how hardware works. It is the difference between one who is product oriented (deals in reality) and the antonym of a product person - the MBA. DBLEXPOSURE posted wild speculation - even worse doing so without first reading a previously posted and technical answer. Two problems in his response are cited. But then he adds a third problem: learns only half of how a CMOS date time clock works; speculates that timing changes in the OS changes a date time clock.

First what he (and others) originally posted in response to do_not_spam_me's original question has nothing to do with the question asked by do_not_spam_me. Second, many of those posts all but admit they don't know - based in wild speculation.

At least, in a later post, DBLEXPOSURE attempts to learn how the CMOS date time clock works. But he still got it wrong. Those applications - "Likely culprits" - will not affect the battery backup CMOS date time clock. He should have known that even from facts that an inquisitive user observes.

BTW, Rick Yerger also criticizes DBLEXPOSURE for not answering the question. Rather than act product oriented, DBLEXPOSURE replies as an MBA:

Again he demonstrates no grasp of facts - instead using feelings as if his feelings were facts. I don't have anything to apologize for when I criticize what DBLEXPOSURE and others have posted. Wild speculation was misrepresented as fact - and did not even answer do_not_spam_me's question.

Two factors cause significant variati> Why is speculation useless? Nobody can give one solid answer because

If there was an answer in this thread, I must have missed it. So many ideas, so few applications of the facts :-)

There are two clocks in a PC (I don't know MACs) A hardware one, and the software clock. When the PC boots, the BIOS reads the hardware clock, and the OS asks the BIOS what time it is. From there on, good old windows or whatever is doing the clock counting, using an interrupt timer. Given the sloppy programming, and the inability of windows to pre-emptively multitask, the software clock is not going to be very accurate. Just open your time settings screen and watch the second hand on the clock. That will show you right away that not only is windows terribly inefficient, it is unable to update the clock consistently, and accurately, even when it is 'idling,' due to system overhead, poorly implemented.

Each time you power down or restart the PC, the hardware clock is read, and it is more accurate than the software, although still subject to crappy crystals and poorly implemented devices. If you leave the computer on for days at a time, a restart will probably get the clock back to a more accurate setting, but not necessarily much better.

The question of why the PC clock is so inaccurate, and yet more expensive than a cheapo watch is simply a matter of "how ya gonna get the information out of the cheap watch, and into the PC?" The clock itself, and the crystal are only a portion of the hardware required by a PC to know what time it is. The additional requirements increase the sicon die size, as well as the complexity of the design, so the higher cost is to be expected. If you can get the time out of a cheap watch, in binary form, at the proper levels, and the proper timing specs, without raising the price of the $1 watch, a lot of people would like to hear from you ;-)

There are many sources of RTC boards that plug into a PCI slot and take over the timekeeping for highly accurate applications, and of course, as so many pointed out, apps the use the National Standards are free and easy given net access.

Just another 3.5 cents.

Mark

Incorrect.

That wasn't the question. The OP didn't ask how to solve the problem.

The truth is, I could care less about what you think about what I say. You are in no position to tell me what I should or what I should not do or have done. If you where a man worth listening to, you would simply post your opinion with no need to tell others how they should or should not have written there post. Truth is, you get off on taking jabs at other rather than simply posting what you think, (typical of a NG twit who cannot be aggressive in the real world for fear of getting bones crushed) Oh, and by the way, What you think it not, nessiccarily the only opinion that counts or matters. So, like I said before, f*ck you! And I'll post answers in what ever fashion I wish and I will be the judge whether what I post is relevant to the conversation. I don't need you to tell me that either.

Who the f*ck do you really think you are? Cause you aint shit to me....

And by the way, your little game of taking bits and pieces of previous threads is as annoying as the five second sound bite that removes the true context of the conversation and twists the words to suit your own purpose. It is quite transparent as we can all go back and read the thread as it was originally posted. Idiot.

Truth of the matter is that the program, "D4" is relevant to this conversation as somebody else may come along and read this thread who never knew the situation could be correct with a small transparent bit of software. That person may appreciate the fact that I brought that subject to the table. Oh, and By the way, the OP might as too. You see, the world doesn't revolve around you and what you think..

Oh, and here is my complete response to Rick Yeager

So what? I had offered an answer to that as well as offering a solution. Perhaps you didn't read that part of the thread.

Now, Had I said your pc's clock will run slow because magic trolls and ferries sneak in make adjustments to the master oscillator. That might warrant an attack. But the rest of this crap is just that, crap!

you see my mind is not one dimensional, I might take a question and expound on the answer to not only give a reason why this happen but also offer a way to correct it.

And by the way, my last comment was prefaced, "Just in case anybody is interested". Obviously you are not so the post was not intended for you. In other words, Bug Off, pedal on and get a life!

You took 8 word out 4 paragraphs... Who do you really think you are?

I'll ask you again to kindly f*ck off.......

Could you have a look into how these clock are constructed.. ?

The answers I found useful in the thread are: * Use internal capacitor to adjust for the crystal. * Provide stable voltage. * DS1387 (suns?) have a good track record. * Crystal chassi shall be grounded.

Useing these facts it should be possible to construct a fairly precise clock. A precise crystal with internal capacitor in shielded box powered by it's own linear voltage regulator should do it?

It could then countup a synchronous counter on positive flank. And be read on negative flank (and only then).

Regulator could use diodes to enable proper batteri/psu operation. Separate regulator for counter and crystal.

D

How about offering some insight rather than just a big buzzer?

Depends on the version really, Win 3.1 and earlier didn't offer pre-emptive multitasking, when an application was minimized it generally ground to a halt. Win 9x was a big improvement over this but still mediocre. Win NT/2K/XP is better still, and are generally quite good OS's, but the multitasking is still rather poor compared to several other OS's on the market. Of course any OS is a compromise, what you gain in one area you often lose in another.

Poor calibration at the factory, and the fact that the clock time is often a blend of RTC time and various real or imaginary timers inside the OS.

-- Transpose mxsmanic and gmail to reach me by e-mail.