How does your OS know the right time?

[MeddyDuo]

If you don't have an Internet connection, and you just installed XP, how does XP know what time is correct? You can select which timezone you are in, but if the BIOS clock was wrong, wouldn't the OS clock be wrong then too? Or do you have to set the time when you are installing XP (I can't remember)?

 

[Schadenfroh]

The bios time is the most important time.

 

[MeddyDuo]

Another question, does the BIOS clock keep going even when the mobo is just in the retail box? That's what the battery is for, right?

 

[blackangst1]

Originally posted by: MeddyDuo
Another question, does the BIOS clock keep going even when the mobo is just in the retail box? That's what the battery is for, right?

Correct. However, most bios's dont come correctly set from the factory.

 

[corkyg]

With an Internet link, getting the exact time is easy. However, with no link, you can still do it. Set your watch exactly using the telephone and then set that time into your PC. You usually can get within a few seconds.

I use a utility called 1st Clock that does all this automagically with an Internet connection.

1st

 

[Bill Kunert]

XP also does it automatically.

 

[Bob Anderson]

Originally posted by: MeddyDuo
If you don't have an Internet connection, and you just installed XP, how does XP know what time is correct? You can select which timezone you are in, but if the BIOS clock was wrong, wouldn't the OS clock be wrong then too? Or do you have to set the time when you are installing XP (I can't remember)?

Here's how time is controlled:

A Germanium crystal beating at 32,768 Hz passes this frequency to a Real
Time Clock (RTC), the RTC being powered by the on- motherboard 3.3 v Lithium
battery. The RTC passes its signal to the BIOS, which then passes it to the
OS. An in- spec crystal will keep time to +- 1 minute / month.

If the Lithium battery dies and the computer is not plugged in to AC, then the BIOS date and time will revert to a value such as January 1, 2000 and it will have to be reset in the BIOS. An OS can offset the time from the BIOS as you see it displayed in the OS, but this does not effect the BIOS time itself.

-Bob

 

[greylica]

Windows XP only corrects the time if your clock is set to the day you are. The sinc will only give you the correct time in your zone.

 

[Fullmetal Chocobo]

Originally posted by: Bob Anderson

Originally posted by: MeddyDuo
If you don't have an Internet connection, and you just installed XP, how does XP know what time is correct? You can select which timezone you are in, but if the BIOS clock was wrong, wouldn't the OS clock be wrong then too? Or do you have to set the time when you are installing XP (I can't remember)?

Here's how time is controlled:

A Germanium crystal beating at 32,768 Hz passes this frequency to a Real
Time Clock (RTC), the RTC being powered by the on- motherboard 3.3 v Lithium
battery. The RTC passes its signal to the BIOS, which then passes it to the
OS. An in- spec crystal will keep time to +- 1 minute / month.

If the Lithium battery dies and the computer is not plugged in to AC, then the BIOS date and time will revert to a value such as January 1, 2000 and it will have to be reset in the BIOS. An OS can offset the time from the BIOS as you see it displayed in the OS, but this does not effect the BIOS time itself.

-Bob

Nice post. :thumbsup:

 

[Bob Anderson]

Fullmetal Chocobo:

Thank you.

I might as well take this opportunity to list the three reasons why computers fail to keep proper time inside of the +-1 minute per month design specification:

a) a weakened Lithium battery means the RTC cannot interpret the crystal frequency correctly;

b) the Germanium crystal itself is chemically impure and does not beat at the correct frequency;

c) the oscillator frequency in the RTC is incorrect due to an incorrect capacitive load between the crystal and the RTC oscillator. If the capacitive load is less than the crystal was designed for, the oscillator runs fast. If the capacitive load is greater than what the crystal was designed for, the oscillator runs slow.

Items b and c are common in consumer- grade motherboards.

-Bob

 

[thegorx]

actually computers take a readings of the position of celestial bodies and can calculate the time, not really, but if the bios dies you can always use your desktop as a sun dial

And yes it's true IBM built stonehedge