[time-nuts] Accurate timestamping on computers (previously: For mywhole life timezones have been weird)
Michael Tharp
gxti at partiallystapled.com
Sat Nov 3 15:47:45 UTC 2012
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
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