[time-nuts] Accurate timestamping on computers (previously: For mywhole life timezones have been weird)

[Michael Tharp]

On 11/03/2012 05:05 AM, Sarah White wrote:
> Seeing as I'm in the process of installing a hardware refclock (trimble
> thunderbolt connected via serial port) for my NTP, it is highly
> problematic and potentially error-prone for microsoft's OS to touch the
> bios hardware clock AT ALL.

Just in case it isn't perfectly clear from the other replies, the 
hardware RTC is not used for timekeeping while the system is running. 
There are a number of other timers in your typical PC which are used for 
actual operational purposes, e.g. HPET and TSC. These tick fast enough 
(>10MHz) that the OS kernel can "discipline" them in software by 
altering the number of ticks considered to comprise a second. As far as 
I know none have a voltage-controlled oscillator but that would 
certainly be interesting :-)

The RTC's current purpose is to keep time while the system is off, as it 
can run for many years from a lithium coin cell, and to wake the system 
at a scheduled time if desired. Adjusting the RTC will have no impact 
whatsoever on the running system clock(s) and, as pointed out elsewhere, 
internally even Windows keeps time in UTC. That said, I'm all for 
storing UTC in the RTC for more practical reasons, e.g. dual-boot 
compatibility and avoiding shenanigans if the power is cut during the 
changeover window. Maybe someday they will be sufficiently motivated to 
cut their ties to the past.

-- m. tharp