explain xkcd - User contributions [en]

Talk:1175: Moving Sidewalks

2013-02-19T16:30:29Z

86.82.116.63:

I'm not quite sure what the joke here is supposed to be. Many have tried to develop variable speed walkways, as one can see in [http://worldwide.espacenet.com/searchResults?page=0&compact=false&ST=advanced&locale=en_EP&DB=EPODOC&CPC=B66B23%2f26%2flow patents]. There was even a pair of these that were installed circa Y2K in the Paris subway (Châtelet-Les-Halles, IIRC), which is renowned for its long passageways. It is AFAIK no longer in service, I don't know why. When I saw it an attendant was present to watch over for making sure that users wouln't fall. This contraption is way more complicated than standard rubber-belt conveyors with its meshing steps. --[[Special:Contributions/70.52.115.181|70.52.115.181]] 15:59, 18 February 2013 (UTC)

I know what I'm building this weekend... [[Special:Contributions/207.237.164.241|207.237.164.241]] 06:22, 18 February 2013 (UTC)
:I just wonder if it is possible to remove these stupid posts and the panel on top of them from my treadmill without breaking it... {{unsigned|89.174.214.74}}

Isn't "of" suppose to be "off" in the title text? {{unsigned|67.161.114.84}}

Do anybody know examples of such belts. The ones I recall has all one-speed-only [[User:Spongebog|Spongebog]] ([[User talk:Spongebog|talk]]) 10:43, 18 February 2013 (UTC)
: At Toronto Airport they have double speed moving sidewalks, that accelerate by stretching the panels. --[[User:Johnsmith|Johnsmith]] ([[User talk:Johnsmith|talk]]) 08:43, 19 February 2013 (UTC)

I was under the impression (from the alt-text), that they would take the belts inward traveling faster until they hi-five. Then, as they sped away, they would change sides and repeat the process. 10:56, 18 February 2013 (UTC)

I don't see why they are positioned as they are. If they were taking the belts inward, they would take advantage of the momentum imparted by the belts and be going much faster than their stride would normally take them. The way they are positioned, they would have to be running to just catch up to each other in the middle. [[Special:Contributions/64.121.163.170|64.121.163.170]] 11:06, 18 February 2013 (UTC)

:This is surely the point. They have to run faster as they get closer. [[Special:Contributions/77.99.26.23|77.99.26.23]] 12:00, 18 February 2013 (UTC)
:: Has the picture changed? Now it seems as if they where going faster to the middle. --[[User:Johnsmith|Johnsmith]] ([[User talk:Johnsmith|talk]]) 08:48, 19 February 2013 (UTC)

There doesn't appear to be any 'trick' to this one. Like the commenter above, I initially thought they were being taken towards each other by the conveyers. I thought the joke was that they would be accelerated to a ridiculous speed which would make it impossible to high five without obliterating each other, but the alt text didn't indicate anything like this and I looked again and realised I had read way too much into it. It's probably most sensible to interpret the speed multiples as relating to the first belts, not the last one you were on. This makes the difference between the '5x' belts going at 5x the speed of the outer ones, instead of 100x if each was the specified multiple of the last. If this alternative situation were the case, the outer belts would have to be going very slowly (of the order of 0.1m/s) for them to ever be able to high five. [[Special:Contributions/77.99.26.23|77.99.26.23]] 12:00, 18 February 2013 (UTC)

The appears reminiscent of Improv Everywhere's prank, "High-Five Escalator" http://improveverywhere.com/2009/02/09/high-five-escalator/ [[User:JamesCurran|JamesCurran]] ([[User talk:JamesCurran|talk]])

I'm sure I would fall over trying to use this one. --[[Special:Contributions/173.49.75.121|173.49.75.121]] 14:09, 18 February 2013 (UTC)

Randall updated the comic, explaining that he meant to draw the arrows going the way Cueball and Megan are facing, not opposite. I'd change the wiki, but I don't get it now. :) [[User:Zpletan|Zpletan]] ([[User talk:Zpletan|talk]])

The Comic has been changed: "Oops! I originally put up a version with backward sidewalk arrows. I should know better than to edit and post comics while sleep-deprived. Sorry!" [[Special:Contributions/86.32.218.17|86.32.218.17]] 14:28, 18 February 2013 (UTC)

I don't think they're going a multiple of the previous belt, but a multiple of base speed. Just my 2 cents :) Also, I think the belts are moving toward each other to get the ultimate "high five" in terms of velocity of the impact. {{unsigned|161.31.32.81}}

I don't see why anyone would think the "5x speed" etc would mean 5 times the previous tile. Seems obvious to me that the first tile is moving at some speed, the second tile is moving twice that base speed, the third moving 3x that base, etc. So when the pass each other their moving at 10x the base speed. Assuming the base speed is something reasonable, something near a typical walking speed, the high five would take place at a speed similar to if they were just sprinting past each other. Hardly a "ridiculous speed which would make it impossible to high five without obliterating each other." [[Special:Contributions/67.51.59.66|67.51.59.66]] 16:58, 18 February 2013 (UTC)

Does anyone think this may be a reference to "The Caves of Steel" a novel by Isaac Asimov? As I recall there was a global system of moving belts of various speeds that were used for transportation.
: That's what I thought of immediately. [[Special:Contributions/128.84.127.95|128.84.127.95]] 19:17, 18 February 2013 (UTC)
: Or Heinlein's "The Roads Must Roll". [[Special:Contributions/173.8.183.86|173.8.183.86]] 19:41, 18 February 2013 (UTC)
:: Also Clarke's ''The City and the Stars'', for the {{w|Big Three}} trifecta. But in those stories, the different-speed belts were arranged in parallel, like lanes of a highway, rather than in series. So you'd accelerate by stepping sideways from belt to belt.
::[[User:Wwoods|Wwoods]] ([[User talk:Wwoods|talk]]) 20:30, 18 February 2013 (UTC)

Seriously, they're playing a game of Robo Rally [[User:schmammel|talk]]

I would love to see this sidewalk placed in a Bison habitat.[[Special:Contributions/94.191.187.81|94.191.187.81]] 05:04, 19 February 2013 (UTC)

Is it just me - or was this comic fixed after it was initially uploaded? I could've sworn the original had either the arrows backwards or the people on the wrong sides - They would've been fighting the sidewalk. 09:59, 19 February 2013 (UTC)
:As an edit to this, I was correct. This is a mirror of the comic on Gizmodo, showing the error. http://img.gawkerassets.com/img/18f07q9hveoaepng/xlarge.png {{unsigned|‎77.98.193.149}}
:And it seems that when fixing it, Randall changed all the arrows, rather than moving the people. [[User:JamesCurran|JamesCurran]] ([[User talk:JamesCurran|talk]])

I wonder, what is the pace of the centerbelt? Is it 5x, 6x or maybe about 5x where that belt start, accelerating to 7x (or even more?) at the high five location and then slowing down till about 5x at the end? [[Special:Contributions/86.82.116.63|86.82.116.63]] 16:30, 19 February 2013 (UTC)

Talk:1168: tar

2013-02-01T22:33:20Z

86.82.116.63:

I thought the title text would be "tar --help"
[[Special:Contributions/123.202.19.132|123.202.19.132]] 06:59, 1 February 2013 (UTC)

The comic is about the difficulty of the tar program options.

Even if his life depended on it and after years of usage, Bob/Randall could not come up with the right parameters without looking them up. So a situation is shown, where Bob's life depends on coming up with the right parameters:

* It shows an atomic warhead
* It has a user interface, which requests any valid tar command
* If it is not entered on the first try within 10s, the bomb is not disarmed and potentially explodes on the spot

Randall has come up with a situation, where the unix guy Bob can be the hero by knowing tar parameters. This is a pipe dream of a geek; nobody cares IRL, if you know tar parameters on the first try.

It is hilarious, that
* the bomb says in full detail the rules including that you should not cheat and it probably has no means to check whether you cheated. This is no game, but feels like one. In war and love every means is allowed - even cheating; it would also be self-defense for disarming the bomb; Bob and his colleagues are not even considering to cheat.
* the user has root access to the bomb, shown by the bomb as ~#, the tilde is the home directory, the # signifies super-user rights; even if the available programs prevent the bomb from being shutdown or disabled by a nonintended way, normally no root access is given for users of linux devices during normal usage; and disarming the bomb with official rules is normal usage of a bomb; a root prompt should not be necessary, if the bomb software is designed and configured well; possibly the unix prompt is a simulation for entering an answer
* Bob shurely needs more than 10s to come. So the bomb will have announced that questions, which require unix knowledge will follow - or has already asked other Unix questions; perhaps after 10s without entering anything a new question comes up
* this bomb can be disarmed with "common knowledge"

Small notes:
* The screen looks to be really grayscale (esp. the inverted "TEN") - not just because of the comic; it has at least 3 colors (black, white, tar gray); it could be that the "TEN" is updated dynamically and is thus inverted
* The comic is quite black: The screen and the bomb; Randall seldomly uses solid black areas; the bomb is a gloomy topic so it is black like "tar" (pun)

Sebastian --[[Special:Contributions/178.26.121.97|178.26.121.97]] 07:24, 1 February 2013 (UTC)

I think there is a visual double pun in this strip: the bomb disarmed by a tar command is a reference to the [[wikipedia:Tar (computing)#Tarbomb|tarbombs]], but it also looks like the [[wikipedia:File:Tsar Bomba Revised.jpg|Tsar Bomb(a)]]. --[[User:Koveras|Koveras]] ([[User talk:Koveras|talk]]) 08:24, 1 February 2013 (UTC)
: I don’t think it looks like Tsar Bomba. If anything, it is much more similar to [[wikipedia:Fat Man|Fat Man]]. --[[User:Mormegil|Mormegil]] ([[User talk:Mormegil|talk]]) 08:38, 1 February 2013 (UTC)
:: Yeah, but "Fat Man" doesn't sound like "tarbomb". --[[User:Koveras|Koveras]] ([[User talk:Koveras|talk]]) 10:48, 1 February 2013 (UTC)

I think another joke is in the fact that you don't know which Unix is running on the bomb so you don't actually know which parameter layout is supported. tar --help for example may or may not be valid since -- is a GNU extension.

tar -bvzx for a tar.bzip2 .... wait... no... argh... I've always just trusted my fingers.. --[[Special:Contributions/59.167.191.93|59.167.191.93]] 10:14, 1 February 2013 (UTC)
: Will '''tar -?''' be valid everywhere?. [[User:Arifsaha|Arifsaha]] ([[User talk:Arifsaha|talk]]) 19:32, 1 February 2013 (UTC)

tar -lvvb archive.tar.bz
File not found. Sorry, you're dead.
~#
[[Special:Contributions/74.82.68.68|74.82.68.68]] 12:35, 1 February 2013 (UTC)

Googling tar commands would definitely take more than 10 seconds, especially considering that Rob did not take his computer. (A smartphone is an option, but...)
Then again, why would "ten" be written in letters instead of numerals? [[User:Greyson|Greyson]] ([[User talk:Greyson|talk]]) 13:28, 1 February 2013 (UTC)

I think the current explantion is missing an important point: the tar commands are not that much difficult. What makes tar complicated is that there are many different implementations. The linux guy knows only gnu tar, but some unices have much different implementations and different commands. "tar --help" is certainly not available on an old hpux, for example. '''That''' make is difficult to type a valid tar command – even more if you don't know the implementation.
[[Special:Contributions/212.222.53.78|212.222.53.78]] 10:26, 1 February 2013 (UTC)
: Will '''tar -?''' be valid everywhere?. [[User:Arifsaha|Arifsaha]] ([[User talk:Arifsaha|talk]]) 19:32, 1 February 2013 (UTC)

I'm a Windows user, so bear with me. Couldn't he type something like "man tar" to get the proper usage of the "tar" command on this particular system? It's a "man" command, so it shouldn't count as a try towards typing a "tar" command. Of course, maybe the bomb would explode if he entered anything else. [[Special:Contributions/70.31.159.230|70.31.159.230]] 13:46, 1 February 2013 (UTC)

:Yeah, all standard Unix installations should have man installed. But many mini installations don't, so these days Google is the standard backup.[[User:CityZen|CityZen]] ([[User talk:CityZen|talk]]) 14:58, 1 February 2013 (UTC)

Randall's joke is spot on, as usual. I've been using UNIX for nearly 30 years. Windows User's solution is elegant. Before Google there was the <code>man</code> command. In all seriousness, productivity on a UNIX box can be greatly enhanced simply by keeping good notes. I keep patterns of all sorts of UNIX commands handy so I don't have to look them up. As Wikipedia implies, <code>tar -tf</code> (I prefer <code>-tvf</code>) should be memorized because one quickly learns that one should ''always'' inspect tarballs before unpacking them. ''– [[User:Tbc|tbc]] ([[User talk:Tbc|talk]]) 14:11, 1 February 2013 (UTC)''

One of the reasons that tar is so useful is that it can often do exactly what you want when other, more obvious commands cannot. For instance, recursively copying a directory from one place to another (using "cp") can be tricky when symbolic links are involved, and thus people memorize incantations like "tar cf - . | (cd dest; tar xf -)". As well, it's a standard tool that's guaranteed to be found on every Unix installation (unlike zip/unzip).[[User:CityZen|CityZen]] ([[User talk:CityZen|talk]]) 14:58, 1 February 2013 (UTC)

tar --help. Problem solved. '''[[User:Davidy22|Davidy22]]'''[[User talk:Davidy22|<tt>[talk]</tt>]] 15:21, 1 February 2013 (UTC)
: Maybe '''tar -?''' is better?. [[User:Arifsaha|Arifsaha]] ([[User talk:Arifsaha|talk]]) 19:32, 1 February 2013 (UTC)

What about "tar xf foo.tar"? I always assume options without dash work everywhere because options they are the original scheme. Of course, foot.tar might be absent, but in my view, the command itself remains valid.
As to the time limit: I imagine a countdown starts when the first key is hit - that leaves little time for "man tar". [[Special:Contributions/46.142.35.251|46.142.35.251]] 16:49, 1 February 2013 (UTC) madd

I think the clock is already counting down. So probably they've discovered the bomb with still some minutes on the display. They call Bob when there is a minute left, He arrives with 25 sec's on the display and 15s later the screendump is made... [[Special:Contributions/86.82.116.63|86.82.116.63]] 22:33, 1 February 2013 (UTC)