[ntp:questions] drift modeling question

Unruh unruh-spam at physics.ubc.ca
Fri Jul 18 21:59:03 UTC 2008

David Woolley <david at ex.djwhome.demon.co.uk.invalid> writes:

>Martin Burnicki wrote:
>> About which operating system(s) are you talking?

>For powered up timing, MS-DOS, its predecessors if they implemented a 
>software clock at all, the MS-DOS Windows (3.0, 3.1, 95, 98, ME, 98SE),
>most, if not all of the NT Windows (NT 3.5, NT 4.0, Windows 2000, 
>Windows XP, probably Windows 2003), Linux from start to 2.4, and mostly 
>for 2.6, SCO OpenServer.......

>(The tick rate for MS-DOS family systems is a good clue to which timer 
>they use.)
>> The PC's standard RTC chip can certainly generate cyclic interrupts.
>> However, if a cyclic interrupt from the RTC or from another timer chip is

>But generally isn't used for that.  ISTR that some early PCs didn't have 
>an RTC and had to be set when booted.

>> used to drive the scheduler depends on the type and eventually on the
>> version of an operating system, isn't it? 

>Divergence into alternative periodic sources on IBM PC type machines is 
>very recent.

There is the rtc, and then there is the timer chip on the PC board. I
thought that they were very different. The RTC is the on board real time
clock powered by a battery on the cmos. The timer interrups are a divisor
of the main bus clock that drives the computer bus I believe. I thought we
were talking about the rtc, not the bus clock. ( int 8 not int 0)

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