The Database of the Time Lords

Time zones have been a necessity since humans could travel faster than a horse, but with computers, interconnected over a vast hive of information, a larger problem has emerged. How do you keep track of time zones? Moreover, how do you keep track of time zones throughout history?

Quick question. If it’s noon in Boston, what time is it in Phoenix? Well, Boston is in the Eastern time zone, there’s the Central time zone, and Phoenix is in the Mountain time zone; noon, eleven, ten. If it’s noon in Boston, it’s ten o’clock AM in Phoenix. Here’s a slightly harder question: if it’s noon in Boston, what time is it in Phoenix during Daylight Savings Time? Most of Arizona doesn’t observe Daylight Savings Time, so if it’s noon in Boston, it’s 9 AM in Phoenix. What about the Navajo Nation in the northwestern part of Arizona? Here, Daylight Savings Time is observed. You can’t even make a rule that all of Arizona is always on Mountain Standard Time.

Indiana is another example of bizarre time zones. For most of the 20th century, Indiana was firmly in the Central time zone. Starting in the 1960s, the line between Eastern and Central time slowly moved west from the Ohio border. Some countries opted not to observe Daylight Savings Time. In 2006, the entire state started to observe DST, but the northwest and southwest corners of the state remained firmly in the Central time zone. The odd geographic boundaries of time zones aren’t limited to the United States, either; Broken Hill, New South Wales, Australia is thirty minutes behind the rest of New South Wales.

Working out reliable answers to all of these questions is the domain of the Time Zone Database, a catalog of every time zone, time zone change, and every strange time-related political argument. It records Alaska’s transition from the Julian to the Gregorian calendar. It describes an argument in a small Michigan town in 1900. It’s used in Java, nearly every kind of Linux, hundreds of software packages, and at least a dozen of the servers and routers you’re using to read this right now.


The idea of daylight savings time was first suggested by Benjamin Franklin in a 1784 essay to the Journal de Paris. An Economical Project for Diminishing the Cost of Light suggested that by simply moving the clocks forward and backward in accordance with ‘sun’ time, fewer candles would be burnt at night. Over the course of a year, this would save the city of Paris sixty-four million pounds of candles. Franklin also suggested posting guards in the shops of candle makers so no family would be permitted more than one pound of candles per week. It was also suggested that all church bells ring at the crack of dawn, and cannons be fired in every street, to wake the sluggards and squeeze every last drop of productivity from the populace.

The first serious publication suggesting a deviation from solar time was A System of National Time for Railroads, published in 1870 by Charles Ferdinand Dowd. This proposal, given to superintendents of railroad lines at the time, set out time zones across the United States, although the details were a bit fuzzy. Years later, troubles with where to place these time zones were worked out. On November 18th, 1883 — the Day of Two Noons — church bells rang twenty-four times in an hour.

Deep in the recesses of the time zone database — most often called tz or just zoneinfo — lie hundreds of interesting observations and anecdotes about how time is, or was, observed in different parts of the world. For example, in the 1990s, the Amundsen-Scott station at the South Pole used the same time zone as the McMurdo base on the coast. However, because the generators run at 60.1 Hz, the clocks had to be set back five minutes every few days. In the early 2000s, Brazil’s daylight savings time was delayed in years with elections. Since Brazil uses electronic voting machines that cannot have their time changed, the country cannot change from standard to daylight savings time between the first and second rounds of elections. The solution to this problem is either change the date daylight savings starts, change the voting machines, or change the constitution.


The creator of the time zone database is Arthur David Olson, who, in 1986 created a tool to easily parse different time zones, and the dates they were in use. For example, the time zone ‘compiler’ will parse a human-readable table, and spit out what time zone applies at what point in history:

# Zone	NAME		GMTOFF	RULE/SAVE	FORMAT	[UNTIL]
Zone	US/Hawaii	-10:30	USA		H%sT	1933 Apr 30 2:00
                        -10:30	1:00		HDT	1933 May 1 2:00
                        -10:30	USA		H%sT	1947 Jun 8 2:00
                        -10:00	-		HST

This bit of code applies the normal USA daylight savings rules in Hawaii until April 30, 1933, then do a Hawaii’s day’s worth of daylight saving, then switch back to standard rules until June 8, 1947, and finally go on to permanent standard time. All of this is exquisite in its completeness and sublime in its readability.

Since 1986, the loose amalgamation of time zone volunteers grew, and in 1993, a proposal for standardized names for time zones was submitted by Paul Eggert. You’ve seen these names before, hidden deep in the time and date settings of your Linux distribution, OS X, and even some Macintoshes going back to at least Mac OS 8. Every time zone is defined by a name in the format of MAJOR_REGION/COUNTRY/CITY, such as North_America/US/Los_Angeles and Asia/Afganistan/Kabul.

With the human and machine-readable compiler and some sort of organizational nomenclature, the modern Time Zone Database was more or less set up by the mid-1990s. After that, it was only a matter of finding where and when time zones changed and bringing them into the database. This is not an easy task; in 2015, no one knew when daylight savings would begin in Morocco. This was originally ascribed to an incorrect news report, but more investigation revealed a version of the database from 2012 incorrectly predicted Morocco would fall back on the last Sunday in September.


But where do these updates come from? Who scours the news for mentions of changes to daylight savings time. An army of volunteers, with a peculiar hobby. Or at the very least knowledge of how the time zones in your computer are actually updated. Simply by sending a few emails, anyone can relay the fact that a dictator doesn’t want to wake up before dawn, or a country is changing time zones because of a drop in oil prices.

Time is the most fundamental thing any of us will ever deal with. However, because no one really wants to get up too early, we’ve invented clocks, time zones, and politicized it. Time, thanks to railroads and agriculture, are in flux, and every change in time zones is recorded in the time zone database. It is the database of the time lords, and one of the most significant historical documents found on every Linux distribution.

72 thoughts on “The Database of the Time Lords

    1. With India and Bangladesh using different time zones and a very complicated “border” (pockets of Bangladesh inside pockets of India inside Bangladesh and vice-versa) I wonder how that works out?
      B^)

  1. Clearly Benjamin Franklin was an arsehole with a predilection for getting more done in the morning and no sympathy for those whose bodies and minds preferred the opposite. I bet he was a “sluggard” himself during the evenings and nights when some of us our in our prime.

    Anyway, besides all that I really don’t think DST makes any sense. Think about it. Every business has the right to determine it’s own hours of operation. Every self-employed individual determines when to start and when to stop the days work. The time on the clock is just a number. Had there never been a DST we probably would just have businesses opening up and closing on an lower numbered hour. It’s certainly not in their interest to “burn more candles [or watts]” is it? All DST does is create a bi-annual disruption of our circadian rhythms which for those of us who don’t naturally match those of our morning-people overlords are already stressed!

    I only hope that as the length of DST keeps getting increased towards it’s inevitable goal of being a year-round affliction we might all just move our starting and closing times back an hour and end this painful nonsense!

    1. AIUI,
      Benjamin Franklin woke “early” one morning in Paris, it was daylight, only the earliest of Parisians were about on the streets. Then later, most of the people awoke and went about their business into the night hours. His proposal, albeit tongue-in-cheek, made sense; get the people up and about earlier, and therefore not use so many candles/oil lamps.

    2. DST moves an hour from the morning when most people aren’t doing much, to the evening where people live their lives after work. You get long summer evenings full of light in which you can socialise or get stuff done. All the cruft around DST being ‘nothing but an energy-saving scheme’ completely misses the social aspects of it.

      Anyway, nothing is stopping the curmudgeons from shifting their business hours to ‘keep things the same’, but approximately zero businesses do (with the exclusion of animal farms).

    3. > Every business has the right to determine it’s own hours of operation.

      Actually there are legal restrictions on trading hours in some countries, and contract agreements with shopping centres (of course you might say the shop chose to enter into the contract, but the law is less optional)

    4. Packard:
      Thank you for the statement in the 1st paragraph. All these decades, I was made to believe by the “daytime people” world that there was something wrong with me and I am “just lazy”. Sigh… In fact, I’ve been out of sync with the “daytime people” world since I was 14 years of age and seem to function best at hours well into the morning. I seem to sleep best, mentally and physically, between the hours of 6 AM and 12 PM. Never being able to get to sleep before 3 or 4 AM and always having to get up to partake with the “daytime” folks with only 3 hours of sleep. Talk about exhausting.

      Peace and blessings.

    1. Well, only really if somehow nobody noticed it for a very long time. The changes wouldn’t immediately be propagated to every Linux machine in the world or anything like that — each machine has its own complete copy of the package that only gets updated once in a while depending on the system’s update procedures.

      1. Yes, this is one of the robust features of maintaining a package that is pulled from. The only downside is that changes won’t propagate if updates are not pulled on each system. But the benefit is that mistakes or mischief can be caught before they reach the entire world.

  2. I personally subscribe to a timing system where the legnth of the light part of the day is always exactly 12 hours and the dark time is also exactly 12 hours. The legnth of the hour changes depending on the lattitude, season, and longitude.

    1. The Roman Empire did that. Sunrise at 6 sunset at 6. Jam karet, rubber time.
      Some of us still are encumbered with their math (no zero) hence the lack of a zero hour and those 2 separate halves of the day not numerated (Ante/Post) instead of numbers only. Some cannot count and do integer math because of this.

  3. I’d like to add my name to the list of people who have suggested a separate link for proofreading suggestions, so as to not to clutter up the comments:
    “squeeze every last drop of productivity from the populous” should be “populace”

  4. You got the time history of Indiana right. Most Hoosiers don’t know that we were originally Central. The reason for the change I believe was network TV and wanting to be with New York timing. I remember when there was a official county time (courthouse clock) and the time on the car clock and and at home that we observed. Here we call it Daniels Stupid Time as our governor now pres of Purdue pushed it on us. Summer noon occurs at 13:50-1:50PM. The new england states are thinking of going to Atlantic time and without summer shifting.

    Most importantly when Indiana was without and then with summer shift, our public utility records show that this causes 5 to 7% MORE energy use. In one word this can be explained. Golf! The occupation of attorneys, lawyers, and congressmen.

        1. And before you jump on my case, there are lots of places that say what time it is *NOW* in EST but don’t give the time zone as an offset.

          Ironically my time zone is also called Eastern Standard Time and I am GMT+10:00 so it depends on which EST you are talking about and yes I agree you can offer more words to describe *which* EST you mean but why not do what the rest of the god damned world does and just offer GMT or do you think your *special* because your American?

          The video at the top of the comments sums it up. You may think it is fine to specify EST because your American and of course every American know EST. Well I know EST to as it’s time title as well but it’s a different time zone. Expecting other people to have your *local knowledge* is just ignorant on HAD’s behalf especially considering the global nature of visitors here.

          To summarize:

          Most countries have an eastern side so is it a surprise that most countries have an Eastern Standard Time. EST is totally ambiguous.

          For any given GMT+x:00 there are several countries in that zone but it doesn’t matter because you then KNOW the correct time which is the point of specifying time in the first place.

          And if you don’t get that then tell me the time here where I am. I am in Eastern Standard Time but not the American one.

          1. Just look at it as some constructive criticism for HAD.

            This isn’t really a “flame” by HAD standards lol.

            Also, I love the z80/Teensy SBC – love to see how you used the teensy to control the Z80 RAM bus.

          2. Hi RÖB:
            Thanks for you comment.

            I’ve been following (some of) the HAD articles for about 2 years now and it amazes me to see how much ego, competition and negativity so many posters have toward the designer, reporter (article author) and other posters. Its really sad that we all can’t seem to come together globally as love and light beings that can treat each other with love, respect and kindness.

            The cabal(s) are on their way out, there are no more “entities” (for 3 years now) to affect people negatively, so we actually have a shot as a global race to move back to a state of global peace, love, joy, happiness, global abundance and prosperity. Its not going to happen tomorrow but it is happening in “baby steps”. :)

            On the Z80AVR project, the schematic shows how access to the Z80 bus is accomplished. I got hung up with some other projects before going to the software development phase but I hope to get back to it soon enough. Although, I may redesign the bus interface and wait-state circuitry.

            Peace, love, light and blessings.

      1. Pretty much everyone in the world knows their local time offset from UTC. Pretty much nobody outside the USA has much of a clue of the USA’s internal system, what the zones are, what abbreviations, and why anyone should care.

        Yep UTC would be a great idea. Any Americans too ignorant to know their own time zone can spend 10 daylight saving seconds on a Google search.

        As far as daylight itself, I bet it’d save a lot of traffic accidents to have more light in the evenings, rather than the early morning when civilised people are asleep. Fuck Ben Franklin, the Chris-Chan looking granny fucker.

        1. Even if the user is unaware of their time zone you can still get it in javascript getTimezoneOffset().

          Such a simple problem to solve but no-one solving it because it doesn’t seem to be a problem for those living in America.

        1. You know what would be really funny? Kind of a Divine joke to mess with us Earth inhabitants. Pause the virtual reality simulation, rotate the Earth on its equator 180 degrees and resume the virtual reality simulation. Then the sun would rise from the West and set in the East and no one would figure out how because it would literally change in the blink of an eye. The passing of time would not be effected, just reversed. But would that mess up the database? Would it mess up those existing sundials? Oh! Would it mess up the people (any worse than the current global “daylight” rules)?? I bet physicists, philosophers, mathematicians, engineers, priests and politicians would be trying to figure that one out for centuries to come … arguing all along the way. LOL

          Peace, love, light and rotational blessings.

          1. Rotating the Earth on its Equator confused me, I thought you meant just moving it 180 degrees or 12 hours, now I realize you meant rotating it pole to pole.

            When I went to Brazil 15 (or so) years ago, I was excited to experience what it would be like to see The Sun in the northern sky. I was disappointed to realize that my mind automatically placed it in the southern sky. My days and (horizons) were too broken up to really notice the transition of The Sun “moving West to East” across the sky.

  5. Since the discussion has gone to the dogs alreadyn 2 notesb
    Germany had 3 mandatory starti g timds which rotated in the 70s to alleve traffic congestion. The airlines found 3 weeks are required to adjust to a 1 hour change. (6 weeks of a poor workforce/thinktank is not a nat’l security issue?)
    I like DST and think we should use it all year, OR adjust it over 4 montbs at 15 minutes per month.

  6. If we’re gonna switch from local time schemes to a single global time scheme like UTC let’s go all in and switch to metric. 100 “metric hours” per day (known as “bubbas”), each equalling about 14 old timey minutes. My local sunrise would be around 30 o’bubba, and I’d head home around 60 to 64 o’bubba. A millibubba is pretty close to a second, so it’s a natural. One solar orbit would be 36.525 kBub. Piece of cake.

  7. I wish they would just leave them alone. PITA dealing with daylight savings time. Also, I wish they would do away with am/pm and just use the 24 hour clock.
    Old Indian saying…only white man would think you could cut 12 inches off a blanket, sew it onto the other end of blanket, and end up with a longer blanket.

  8. Yet in a cave devoid of time references, man seems to gravitate toward a 25 hour day. Although I am that way if I do not get enough data and throughput in my 12/24 hour day. I can be up early for certain rare events but in general my noon is 2-5 pm and finally firing on all cylinders, hate that I am attempting to cure a problem via a call to some company that closed at 4PM EST, american. Companies in the west often are available for a couple extra hours, stretching our day… but easterners seem not so inclined. For all the dna reading and satellite impact statistics we can manage, we seem not to be able to agree on time. It is a conundrum. It reminds me of the humor in measuring; the CIA reoorts that all countries use metric except the US and 2 others, and 2 are lying about it. We are admonished to “eat local.” Time seems local also. (Duh) Perhaps interstate communications in real time ought not be done. It’s like shipping goods. “With fair winds, we may see you in March, or so.” I garden and look forward to Dec 23rd when days begin to grow again. I think I want a 34 hour clock that has only an hour hand and no markings, just a background showing my approximate point in so many (9-14) hours of daylight or dark.

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