Re: Questions about PC clock operations

[tony barry <tony () no-bull co nz>]

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 () cse ust hk 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
>
>
> ---------------------------------------------------------------------------
> This list is sponsored by: Norwich University
>
> EARN A MASTER OF SCIENCE IN INFORMATION ASSURANCE - ONLINE
> The NSA has designated Norwich University a center of Academic Excellence 
> in Information Security. Our program offers unparalleled Infosec management 
> education and the case study affords you unmatched consulting experience. 
> Using interactive e-Learning technology, you can earn this esteemed degree, 
> without disrupting your career or home life.
>
> http://www.msia.norwich.edu/secfocus
> ---------------------------------------------------------------------------
-- 
No Bull Services Ltd
PO Box 51528 
Pakuranga
Auckland

021 413642  09 5768552

http://www.no-bull.co.nz

This e-mail and any attached files transmitted with it are confidential
and intended solely for the use of the addressees. If you have recieved
this e-mail in error please inform the sender by sending a reply and
delete this message.

---------------------------------------------------------------------------
This list is sponsored by: Norwich University

EARN A MASTER OF SCIENCE IN INFORMATION ASSURANCE - ONLINE
The NSA has designated Norwich University a center of Academic Excellence 
in Information Security. Our program offers unparalleled Infosec management 
education and the case study affords you unmatched consulting experience. 
Using interactive e-Learning technology, you can earn this esteemed degree, 
without disrupting your career or home life.

http://www.msia.norwich.edu/secfocus
---------------------------------------------------------------------------