Title text: The universe started in 1970. Anyone claiming to be over 38 is lying about their age.
In computer systems, time is measured starting from some arbitrarily chosen point. That particular time is known as the "epoch" for that system. The UNIX operating system internally uses an epoch of January 1, 1970, and measures the time as a number of seconds from then. Since this was intended only for things internal to the OS (File last modified times and the like), using 1-Jan-1970 was safe, as no UNIX systems existed before that date.
However, since UNIX included a number of system functions to manipulate these dates, some developers mistook them for a general purpose date object, and misused them in applications requiring dates before the epoch, by using negative values. Such usage would inevitably fail; for example, since the value isn't specified to be signed or unsigned, the date might be considered to be far in the future, instead of in the past.
Cueball has clearly misused the system date in some way (probably by using an unsigned data type to store the timestamp, which cannot store negative values (in this case dates before 1970) or doing some other operation that doesn’t support negative values). His friend makes a pun by combining "Epoch" with "Epic Fail" - a colloquial term meaning "a very big mistake was made."
Another problem using the UNIX system date as a general purpose date object is commonly known as the year 2038 problem. At 03:14:08 on 19 January 2038, the 32-bit versions of the Unix time stamp will cease to work, as it will overflow the largest value that can be held in a signed 32-bit number. The 64-bit version "will" expire at 15:30:08 on 4 December 292,277,026,596.
The title text takes the joke to the next level, claiming that the entire universe began when Unix did, and therefore no one could have been older than 38 at the time when the comic was released in 2008. The formula is 'x - 1970', where x is the current year, which would explain the bug, since no earlier dates are possible. This is also similar to Last Thursdayism.
An example of this 2 to the 32nd power time overflow problem includes the Deep Impact spacecraft, which, on August 11, 2013, 00:38:49 (more than five years after the comic), was 2 to the 32nd power tenths of a second from January 1, 2000. There is speculation that a system on the craft tracked time in one-tenth second increments since January 1, 2000 and stored it in a signed 32-bit integer, which then overflowed at some point, similar to the Year 2038 problem.
- [Cueball sits at a computer, staring at the screen and rubbing his chin in thought. A friend stands behind him.]
- Cueball: Weird — My code's crashing when given pre-1970 dates.
- Friend [pointing at Cueball and his computer]: Epoch fail!
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That is why on Unix epoch (the time_t type) is signed type, and covers dates before epoch. --JakubNarebski (talk) 19:52, 5 July 2013 (UTC)
- Ohh, and much more is missing. I did mark it as incomplete. We also have to talk about the time frame the 32bit epoch does cover, and what would be changed by using a 64bit variable. What will happen on 19 January 2038?--Dgbrt (talk) 20:17, 5 July 2013 (UTC)
- The general hope, it appears, is that 64-bit integers will be firmly in place, having ousted the feeble 32-bit integers from the system time. As has been demonstrated in innumerable instances, it's rather difficult to eliminate legacy code from systems due to attempts to support older systems in a backward-compatible methodology. In short, however, it will take time to resolve time. Thokling (talk) 05:34, 22 September 2013 (UTC)
- Rewrite needed
The current explanation barely has to do with the actual topic of the comic. Instead it explains several unrelated qualities of Unix time, and petty much skips over the actual epoch thing. Needs a rewrite. --NeatNit 18.104.22.168 05:59, 8 February 2015 (UTC)
Why would anyone want to take the square root of a timestamp? It is much more likely that Cueballs program just handles negative time values incorrectly. Condor70 (talk) 07:15, 14 November 2016 (UTC)
http://coolepochcountdown.com/ links to this site saying that XKCD captured moment when Unix time counter reached 1234567890, so maybe this comic is released at that moment 22.214.171.124 (talk) (please sign your comments with ~~~~)
- No, that time would occur about a year from this comic's publication (13 February 2009 at 23:31:30 UTC). 607: 2038 was published 8 July 2009, which is about five months too late, and I have no idea how 543: Sierpinski Valentine had to do with Unix time. 126.96.36.199 22:34, 16 April 2019 (UTC)