Re: Questions about PC clock operations

Hi,

To the best of my knowledge the PC calculates time by simply counting
the number of cycles of its timing (do not confuse this term or
references to clock pulses with actual time measurement) oscillator. So
if your PC has a clock speed of 100Mhz (100 million cycles per second)
then when the software which is calculating real time has counted 100
million pulses it increments its real time clock by 1 second. The
problem is that the oscillators in computers are not absolutely accurate
or stable (and it is not necessary for them to be so for the computer to
operate) so the oscillator may be running at 100,000,100 cycles per
second. The software counts 100,000,000 pulses and increments its 1 sec
counter but is too early by 100 / 100,000,100 seconds which is a fairly
small error but repeated every second it becomes significant. Now we
will complicate things further by adding in some temperature drift lets
say 10 cycles per second per 1 degree C change in temperature and there
you have your drifting clock.
It should be clear from the above that the drifting clock has nothing to
do with the OS.

Hope this helps.

Tony

On Tue, 2006-08-29 at 06:05 +0800, ricci@xxxxxxxxxx wrote:
Hello All,

As you know time is a piece of information critical to digital forensics
investigation. However, as the paper in DFRWS 2006 pointed out, the PC
clock is not steady but drifting.

So can any one let me know how the PC clock operates? Is there any
difference between the time between Linux clock and Windows? Will the
operating system be affecting the clock?

Please advise.

Thx.

Ricci


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