Post by A Friend Post by Kenny McCormack
Yes, I'd be willing to agree that law enforcement has found a way to deal,
and that most other "critical path" social institutions have as well, but
there's a lot of "next tier" institutions that may not have, and it can
lead to confusion. The example that I often deal with is TV schedules
(specifically the type of displays that we are used to seeing on our
cable/satellite screens and/or on computer services, e.g., Sling). These
displays only have one slot available for a given day/time/channel, which
is fine for all but one particular hour of the year.
I noticed early this morning that my Comcast program guide got around
the time change simply by listing the 1 a.m.-1:30 a.m. bloc twice in
succession. The grid was otherwise normal.
You're both right. If the television schedule server uses UTC, then tv
schedules will use UTC with an offset from Greenwich for local time.
Then there's no conflict at 2 am on the day that Daylight Time becomes
effectives or ends.
If the television schedule still uses newspaper layout format, then
there's no concept of time zone nor Daylight Time.
This all goes back to decisions that were made in the architecture of
the earliest chipsets for personal computers, which nobody was ever
going to use in a real-time computer network. In the beginning, hookiing
up modems meant hideously expensive long-distance calls and files were
transferred from one computer to the next by a computer operator physically
transferring physical media.
In all chipsets for personal computers, the Hardware Clock -- Real Time
Clock -- CMOS Clock -- BIOS Time stored year, month, day, hour, minute,
and seconds. It was assumed that the localtime standard is used, that is,
dependent upon the geographical location of the computer. RTC is set by
the operating system, and required twice-a-year adjustment for the period
in which Daylight Saving Time is in effect. If the Hardware Clock was
used as the clock for any servers running on that machine, then clients
on the user's computer, if in another time zone, had to be aware of the
time offset between the two machines.
Only in chips manufactured since 2016 has firmware been able to store
timezone and use of Daylight time.
The System Clock -- the software clock -- exists in Unix and Linux systems
and modern MacOS's (which is based on Linux). It uses the Unix Epoch,
for which Time Zero is January 1, 1970, midnight at the start of the
calendar day in Greenwich. It doesn't have a concept of leap second and
thus isn't literally UTC, so that requires an adjustment at synchronization
with an Internet Time Server. The Linux kernel counts the number of timer
interrupts since bootup.
Note that the two clocks run independently of each other.
What is typically done at bootup: The operator sets the Hardware Clock
in BIOS to an approximate localtime. The System Clock is set from the
Hardware Clock with information about location, thus setting time zone
(offset from Greenwich) and use of Daylight time, and an Internet time
server is chosen. In 2016 and newer chipsets, this will set timezone and
use of Daylight time in the Hardware Clock as well. The System Clock can
be synchronized if the approximate time is within a few hours. There is
a calculation made in software as to the time it takes for the signal to
be sent from the server to the local machine. The Hardware Clock is then
set from the System Clock after each synchronization with the Internet
At synchronization with the Internet time server, the hardward clock
should be reset automatically from the System Clock.
Why do we have Standard Time at all? Railroads in the UK found it too
difficult to operate without the conductor keep time based on setting
his watch accurately to the station clock at each terminal, which was
set to London time. They standardized on Mean Time at the Royal
Observatory at Greenwich.
Communities along the way would typically use local solar time, setting
clocks at noon based on a sundial. But local apparent noon is at a
different time in each community based on longitude.
Why Greenwich? Ship navigation required being able to calculate
longitude, which required accurate time keeping. (Latitude was
calculated based on observation of the sky.) Because the UK was a
mercantile and naval world power, it had numerous navigation maps based
on Greenwich at Zero Longitude.
Standard Time came to the United States and Canada based on a series of
railroad conferences, culminating in a final railroad conference in
Chicago in 1883. There was some debate as to whether to standardize on
Greenwich or the Naval Observatory in Washington, but again, as there
were more navigation maps based on Greenwich as Zero Longitude, they
went with the British system of Standard Time.
It took decades for standard time to be used as local civil time
throughout the United States, though.
Because of Standard Time's railroad origins, Time Zones in the United
States were set by the Interstate Commerce Commission (today by the
Secretary of Transportation since the ICC sunset). States are assigned
to time zones. If there are states in two time zones, the time zone
boundary is set to county lines. When petitioned to change time zones,
the federal government considers whether local commerce is more heavily
associated in one direction or the other and petitions aren't always
UTC is set in the United States by a combination of the Navy on behalf
of the military and Commerce Department National Institute of Standards
and Technology for civilian purposes, but you know, it's coordinated
The period in which Daylight Saving Time is observed is set in federal
law, but states have the option of implementing it statewide or within a
time zone, thus we had the now-deprecated Indiana Time Zone in which
most of the state's counties were in Eastern Standard Time and did not
observe Daylight Time. This changed a number of years back. Because
Indiana is so far west in EST, during EDT, parts of the state are almost
on double daylight time. Counties in CST always observed Daylight Time.
Alaska and Hawaii remain on Standard Time throughout the year. Arizona
remains on Standard Time, except certain Indian reservations observe