Main Page

Explain xkcd: It's 'cause you're dumb.
(Difference between revisions)
Jump to: navigation, search
(add number of missing comics :))
(Latest comic: update edit link)
Line 11: Line 11:
  
 
<div style="border:1px solid grey; background:#eee; padding:1em;">
 
<div style="border:1px solid grey; background:#eee; padding:1em;">
<span style="float:right;">[{{fullurl:1091: Curiosity|action=edit}} '''edit this explanation!''']</span>
+
<span style="float:right;">[{{fullurl:1092: Michael Phelps|action=edit}} '''edit this explanation!''']</span>
 
<br clear="right">
 
<br clear="right">
 
{{:{{LATESTCOMIC}}}}
 
{{:{{LATESTCOMIC}}}}

Revision as of 13:31, 8 August 2012


Welcome to the explain xkcd wiki! We already have Expression error: Unrecognised punctuation character ",". comic explanations!

(But there are still Expression error: Unrecognised punctuation character ",". to go. Come and add yours!)

Latest comic

edit this explanation!

PermaCal
The flood of PermaCalNTP leap-second notifications was bad enough, but when people started asking for millisecond resolution, the resulting DDOS brought down the internet.
Title text: The flood of PermaCalNTP leap-second notifications was bad enough, but when people started asking for millisecond resolution, the resulting DDOS brought down the internet.

Explanation

This comic proposes a new calendar system. This is similar to comic 1061: EST. In this new calendar system, the date stays constant, and only changes with leap days. This means that all days are now leap days. PermaCal is a portmanteau of the words "permanent" and "calendar".

In the comic, the real date is Monday April 20, 2015 (the date the comic was published). Cueball has not yet added a leap day to PermaCal today, so his calendar still states it is Sunday April 19. Upon learning from Megan that the date has changed since yesterday, he is now forced to add another leap day (and is presumably becoming frustrated that he has to do this every day).

Leap days in the Gregorian calendar are days added to the end of February every year that is a multiple of 4, but not by 100, unless it's also a multiple of 400. The purpose is to synchronize the calendar with Earth's orbit without having a partial day each year. Leap seconds are necessary because the earth rotation is not constant, but speeds up and slows down over time. The leap seconds account for the differences in the length of our 24 hour day and a solar day (the time taken for Earth to rotate so the same point points towards the sun), and are announced several months before hand.

NTP servers are used to keep local computer time from drifting. In the context of this comic Leap seconds would refer to a system with constant time, and the time is adjusted by an NTP call every second. The title text refers to the bandwidth used by correcting the time in every millisecond resolution which for a system with constant time would result in 1000 updates being requested every second using significant network bandwidth and resulting in a DDoS situation.

See here, an example of a real-life unintentional DDOS attack involving NTP servers.

Part of the humor stems from the problems that leap seconds are causing for some computers. [1] The last leap second disrupted computers at big companies such as Reddit, LinkedIn, Gizmodo and FourSquare. Google has coped by adding microseconds stretched out over the year, rather than a single disruptive second, possibly the reason for the reference to millisecond resolution.

Transcript

[Megan and Cueball are in the panel. Cueball appears to be holding a phone, tapping.]
Megan: What day is it?
Cueball: Sunday the 19th.
Megan: But you said it was the 19th yesterday.
Cueball: It changed again? Crap, better add another leap day.
[Caption below the panel:]
My simplified calendar system assumes the date never changes, then corrects any drift via leap days.

Trivia

  • The "H" in Megan's version of "19TH" is missing the upper part of the left bar, making it look like an mirrored "h". This must be unintended, since the H in "19TH" is written correctly when Cueball says it. Also only capital letters are used in the comics (except in special cases).


New here?

Feel free to sign up for an account and contribute to the explain xkcd wiki! We need explanations for comics, characters, themes, memes and everything in between. If it is referenced in an xkcd web comic, it should be here.

  • List of all comics contains a complete table of all xkcd comics so far and the corresponding explanations. The red links (like this) are missing explanations. Feel free to help out by creating them!

Rules

Don't be a jerk. There are a lot of comics that don't have set in stone explanations, feel free to put multiple interpretations in the wiki page for each comic.

If you want to talk about a specific comic, use its discussion page.

Please only submit material directly related to—and helping everyone better understand—xkcd... and of course only submit material that can legally be posted (and freely edited.) Off-topic or other inappropriate content is subject to removal or modification at admin discretion, and users posting such are at risk of being blocked.

If you need assistance from an admin, feel free to leave a message on their personal discussion page. The list of admins is here.

Explain xkcd logo courtesy of User:Alek2407.

Personal tools
Namespaces

Variants
Actions
Navigation
Tools

It seems you are using noscript, which is stopping our project wonderful ads from working. Explain xkcd uses ads to pay for bandwidth, and we manually approve all our advertisers, and our ads are restricted to unobtrusive images and slow animated GIFs. If you found this site helpful, please consider whitelisting us.

Want to advertise with us, or donate to us with Paypal or Bitcoin?