[ntp:questions] drift modeling question

David Woolley david at ex.djwhome.demon.co.uk.invalid
Fri Jul 18 21:14:03 UTC 2008

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.

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