The Unix Timestamp

Time and Dates

Time is a bit of a faff really.

If you want to add 20 minutes to 6:50, you get 7:10. Not, as you would with normal maths, 6:70. I remember at school putting calculators into “clock mode” to add times.

I also remember spending a surprising amount of time during my sound engineering days adding and subtracting times. There was a brief period when I was convinced that we needed to decimalise time; change the system so there are 100 seconds in a minute and 100 minutes in an hour. It will be a bit of a faff for everyone, but if it saves me from having to do slightly tricky mental arrhythmic occasionally, then I’m all for it.

It turns out that computers, similarly, have difficulty with time. Which must be partly why many computer systems use the Unix Timestamp.

The Unix Timestamp is a number. A really long number, like 1369634836 or something. But, ultimately, just a number. And this means that adding and subtracting from it is easy.

The number corresponds to the number of seconds since midnight on 1st January 1970. 1369634836, for example, corresponds to seven minutes and sixteen seconds past 1 AM on 27th May 2013.

Funnily enough, though, the Unix Timestamp was invented until 1971, meaning that the first few thousand numbers only ever occurred in the past. Dates that are before January 1970 are recorded as negative numbers, so theoretically it can go back as far as you want.

These days, the Unix Timestamp is used in loads of, if not all, computer languages.

In javascript, you can generate it with this code:

new Date().getTime();



And so on.

Now, I don’t mean to alarm anymore, but there is an apocalypse coming. Well, I say apocalypse, it’s more just an expensive and inconvenient problem. But on January 19th, 2038, we’re going to have another “Millennium Bug” situation, when the Unix Timestamp gets so big that it cannot be stored in normal (32-bit) computer file systems.

Before this time, we’re either going to have to switch to using 64-bit systems, which support much bigger numbers, or using a different method for storing dates. That is, assuming we there are any 32-bit computer systems still running from today.

Even when we switch to 64-bit systems, though, we’re only prolonging the problem, not solving it indefinitely. At 15:30:08 on Sunday, 4 December 292,277,026,596, we will again run out of numbers. Luckily, though, as Wikipedia notes “This is not anticipated to pose a problem, as this is considerably longer than the time it would take the Sun to expand to a red giant and swallow the earth.”

Which is slightly more of an apocalypse than the dates not displaying correctly on websites really. But I’m still more worried about the date thing than the sun thing.


2 thoughts on “The Unix Timestamp

  1. Pingback: PHP dates – add and subtract months…. really! | steve_kostrey

  2. Pingback: A lot happened on 1st January 1970 | They Had Eggs

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