Sandy Denny 1947-1978 was an English singer and songwriter, lead singer for Fairport Convention. The only guest vocalist on a Led Zep studio album, a duet with Robert Plant for "The Battle of Evermore" on Led Zeppelin's untitled fourth album (1971). Her composition "Who Knows Where the Time Goes?" has been recorded by many artists as diverse as Judy Collins, Nina Simone, 10,000 Maniacs and Cat Power.
(With apologies to Sandy Denny)
Ever thought about where your computer gets the time from?
OK, so you haven't, but I have.
Most people would probably say "From the Internet". Even my Kobo is supposed to set its time "whenever you connect your eReader to the Internet."
But I wasn't satisfied with just "from the Internet" as an answer.
Date and Time
Internet Time tab, where it says "This computer is set to automatically synchronise with
It appears a browser can't load it as a page though. "Problem loading page" says Firefox.
Naturally I'm then clicking in the "Change settings..." button. There I get a drop-down menu of servers: -
What's the bet "nist" stands for national institute of standards time" or similar?
Next was a check at Wikipedia. Sure enough NIST is the National Institute of Standards and Technology, formerly known to me as the National Bureau of Standards, an agency of the United States Department of Commerce.
NIST's Boulder laboratories are best known for NIST‑F1, which houses an atomic clock. NIST‑F1 serves as the source of the nation's official time. From its measurement of the natural resonance frequency of caesium—which is used to define the second—NIST broadcasts time signals via longwave radio station WWVB near Fort Collins, Colorado, and shortwave radio stations WWV and WWVH, located near Fort Collins and Kekaha, Hawaii, respectively.
Now, we know not all computers are in range of those signals, there must be another route for the time signal.
A search for "time.windows.com" on Google gave me a few things:
It is a second-rate time source but only because better is not needed:
Computers that synchronize their time less frequently, such as computers running Windows XP Home Edition, computers with intermittent network connections, or computers that are not joined to a domain, are configured by default to synchronize with time.windows.com. Because they do not synchronize their clock frequently and because the factors that affect time accuracy may not be known, it is impossible to guarantee time accuracy on computers that have intermittent or no network connections.
That was from a Microsoft technical paper about Windows Time Service, used by servers, which need to be synchronised with each other, and need much more accurate clocking.
Now we are getting more techie!
A search for Windows Time Service brings up in Wikipedia: -
"Network Time Protocol" and sub-section Windows Time service
Basically it appears that time.windows.com is not that accurate but it doesn't matter if you are not running a large network. Our little old domestic computers can get by using a system called SNTP, (Simple Network Time Protocol), which is a "simple" version of the full NTP (Network Time Protocol), in use since 1985.
The Network Time Protocol page reminds us how much we rely on just a few dedicated people who actually care about all this:
"Network Time Protocol (NTP) is a networking protocol for clock synchronization between computer systems over packet-switched, variable-latency data networks. In operation since before 1985, NTP is one of the oldest Internet protocols in use. NTP was originally designed by David L. Mills of the University of Delaware, who still develops and maintains it with a team of volunteers."
(Go here for Mills' social-history oriented account of the development of NTP)
Basically they start with an Atomic clock, which drives top level clocks, which drive lower-level clocks etc, with decreasing levels of accuracy. NTP allows a computer to compare several higher clocks and make a calculated compromise as to the time setting.
I particularly like this quote on the Wikipedia NTP page:
"Future versions of NTP may extend the time representation to 128 bits: 64 bits for the second and 64 bits for the fractional-second. The current NTPv4 format has support for Era Number and Era Offset, that when used properly should aid fixing date rollover issues. According to Mills, "the 64 bit value for the fraction is enough to resolve the amount of time it takes a photon to pass an electron at the speed of light. The 64 bit second value is enough to provide unambiguous time representation until the universe goes dim."
Now that's what I call being far-sighted while splitting hairs!
For another far-sighted time-keeping venture, check out the 10,000 Year Clock
Amazing, when the internal clock on my laptop runs at 1.50 GHz, i.e. chops time into 1500000000ths of a second, but can't keep accurate time over a few hours. Proper NTP can tolerate and correct a PC's clock that is out by up to +/- 43 seconds a day. Ordinary watches can be a hundred times better than that. "...a typical quartz clock or wristwatch will gain or lose 15 seconds per 30 days (within a normal temperature range of 5°C/41°F to 35°C/95°F) or less than a half second clock drift per day when worn near the body."