[ntp:questions] drift modeling question

Richard B. Gilbert rgilbert88 at comcast.net
Fri Jul 18 21:26:21 UTC 2008

David Woolley wrote:
> 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.

The original IBM PC and the PC/XT did not have hardware clocks.  If you 
wanted a clock you purchased a "multifunction card" and plugged it into 
the bus.  I believe that the PC/AT was the first IBM PC with a native 
clock.  I have forgotten what else the multifunction card did but it 
supplied a few goodies that were not native.

Clone manufacturers may have beaten IBM and installed clock as standard 

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