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A Story About ‘Magic' (1994) (catb.org)
232 points by ColinWright on Feb 24, 2015 | hide | past | web | favorite | 60 comments



I love things like this.

In my old Dreamcast, I found after I'd packed it up and moved it a few too many times that it wouldn't start, but would show signs of life when the lid would open and close. I found that there was a position you could put the lid in at which it would boot, and that position could be reliably reached if a SweeTart was placed in the tray near the edge of the disc. I licked the flat side of the SweeTart a few times and it stayed where it was, and it's there to this day. Of course, the lock doesn't engage so I have to keep something heavy on top of it.

And on my PS2, I'd fiddled around with it too much trying to mod it, and messed up something in there, but not bad enough that it wouldn't boot and play a game. But about 3/4 of the way through Resident Evil 4, I found it would skip and eventually reset if you didn't tilt it up by 20 degrees or so. As I progressed in the game, the angle at which it had to be set increased, until eventually not only did it have to be tilted in a second direction as well. Believe it or not, it finally reached the point where no tilt could save it in the middle of the final boss, with my friend moving it this way and that like we were trying to get reception with bunny ears on an old TV. I never beat the game.


A friend of mine, working on his PhD in a European university which shall not be named, is using a really old 15 watt ruby laser for some experiments. One day last year it would not turn on, and he and his labmates spent hours trying to diagnose the problem. Finally one of them, exasperated, put his elbow on top of the laser cabinet with a deep sigh, whereupon the laser promptly started working. Excited, they found a big piece of steel and duct-taped it to the top of the cabinet in that very place, with a big "DO NOT MOVE"-note, and the laser has been working fine ever since.


Pragmatic but sad, I expected some nice collective eureka moment after a mental struggle.


Don't look a gift horse in the mouth. (and never invest money in something that eats while you sleep)


Out of curiosity, why does someone studying European history need a 15 watt laser?


European universities teach things other than European history.


The original Playstation had a similar switch on the lid mechanism. I think it was a safety feature to prevent the discs from spinning up, without the enclosure.

When I was about 8-9, I found the mechanism, and ended up dismantling the system. I then wedged a little Wolverine action-figure's foot into the space to keep his foot down on the switch and ran the system without the cover, because it looked pretty badass to have the discs spin out in the open.

[In retrospect: All of this was probably a horribly unsafe thing to do, considering what would happen if the disc cracked or broke while spinning.]


I think it's also to protect your eyes from the CD-reading laser if you were to power it up with no disk in it.


Good point, I actually spent some time staring at that when I was younger. Also found out I needed glasses when I was 10, and my prescription hasn't changed since.


You were fine. The Playstation 1's CD drive spins at only 2x regular audio speed which is no more than 16 Hz rotational speed. It's nothing like the 48x fighter jet turbines of desktop computers. It's only 2x as much as a handheld Discman that has no safety interlocks at all.

All consoles from the PS2 onwards have an enclosed (tray or slot) drive mechanism because they do spin the disc fast enough for safety to be an issue, but the early disc media systems up to the Dreamcast didn't need to worry about it.


The PS2 Slim's disc mechanism is the same as the PS1's (except that it spins faster).


This could also be used to run out-of-region discs on the US market version of the Playstation. It refused to start with a out-of-region disc, but you could start with a US disc and then swap in the out-of-region disc while running, provided it never detected the lid opening.


I had a little spring for mine that clipped over the prong in the lid at one end, and pressed the switch down at the other. You could still open/close the lid, but the Playstation wouldn’t recognise it.


I had an ancient hardcard[0] that was obsolete when I got it in the 90s, but it was the first HDD I owned so it made me very happy. Unfortunately, to get it to spin up, you had to shake the thing vigorously for about 10 minutes, which wasn't such a big deal because there was no case - it was an open benchtop computer.

[0] http://en.wikipedia.org/wiki/Hardcard


Funnily enough we had one of those (or something like it) in the college I went to, also in an open bench top computer. The HD had no cover, and you had to give the disk a spin to get it moving after power-up. Oddly it never suffered ill-erects from environmental contamination of the head / platter. I guess the densities were low enough not to matter so much.


I've just carried a second hand mixer deck home on the bus.

While waiting for my stop, I noticed that if I moved my hand near the left VU meter, the needle would swing. Not much, but a little. It only worked on the left one. I didn't have to touch the case. And no, it wasn't plugged into anything. I'd just ruled out random motion caused by me joggling the deck as I moved my hand when I had to get off.

It doesn't do it any more.


Static Electricity. The meter movement is very delicately balanced, plus the plastic window can become charged. Waving your hand around affects the charge.

You've just invented the Electroscope.


Some nuclear reactor instruments will respond in funny ways if you rub them. I never understood it, but some don't find it very funny.


Way back in the day I did EA Technical Support (on DOS games!)

Anyway the PS2 had a known issue where turning it on its side or over would put the CD closer to the reading laser and "fix it" it was really the only tangible fix the guys in the PlayStation queue had.


Haha, I remember having to turn the original PlayStation upside down to play RE2 because the design placed the motor for the disc tray right under the laser and the heat would cause distortions in the beam ... or so I was lead to believe. Either way, it made the PS play games for another few years. A "magic" button, indeed.


Noticing grammatical errors well after the fact here but I'm glad you guys like the story and have some of your own. That's what I love about electronics that stick with us!


This is awesome in so many ways because it captured the imagination of the people using it. They just saw that switch and actually tried to figure out why it wasn't magic.

Obviously it wasn't, but the way this is written really shows how dumbfound they were because they couldn't explain it.


I would love to have some of those in my office, just to have a psychological change with a flip of a button.



I liked the story because I absolutely love arguing with people who will tell me to trust the map over the terrain. :-|


What does "trust the map over the terrain" mean?


when the map tells you one thing, and your eyes tell you another thing, go with what your eyes tell you, because the map is full of shit.

you would be surprised how often people trust "the map" more than reality. "the map" can be anything, i.e. an instruction manual, an authority figure, folklore, a rumor, whatever.


My dad's friend destroyed film he took of his wedding like that. He developed it himself, water felt hot to his finger but thermometer showed it right. He cooked it.. thermometer was broken. His wife was not amused!


I'd stop and get a third opinion --- because sometimes my eyes are lying.


one more beer, please


Except if you're a pilot flying in low visibility. Then you trust the map, not the terrain (mainly as the terrain is invisible). VFR vs. IFR and all that.


SO your point is that you trust the map only when there's no other option.


In that case your eyes are telling you that they can't see anything and you need to use the map.

Eyes still win!


> go with what your eyes tell you,

but your eyes are also part of the map…



Ah, ok. Thanks.

Reminded me of thinking about what if you targeted a laser on a map and it burned physical terrain.


Was hit by the nostalgia of reading Hackers [0]. What a great prank but quite an extreme dike.

[0] http://www.amazon.com/Hackers-Computer-Revolution-Anniversar...


My favorite was "always mount a scratch monkey":

http://www.catb.org/jargon/html/S/scratch-monkey.html


One of my favourite stories growing up.


Xkcd sells a set of stickers which includes a magic/more magic pair:

http://store.xkcd.com/products/switch-and-button-stickers


I was really really hoping this would be the background of the magic number file "magic", and the `file` command... oh well.

Completely different, but still a fun story.


Ahhh yes, the compulsive need of the reasoning mind to neatly categories all events, circumstances and situations. I just love exploiting that.


I've been periodically thinking about a tattoo based on this story for actual decades. Anyone know of any art based on it?


I love this story. It's mythology from the dawn of Computer Science - like a chapter from Genesis.


great story, although the whole time I was thinking of the appended 1994 explanation. wouldn't that be reasonable? too bad no one thought to measure the magic...


Should be tagged (1994), although it appears the earliest version of this story goes back to Dec 1990!

http://jargon-file.org/archive/jargon-2.2.1.dos.txt


Pretty sure it's older than that I recalled seeing it in this book, which Amazon gives a date of 1983 on (fits well enough with when I recall coming across the book in a public library): http://www.amazon.com/Hackers-Dictionary-Guide-Computer-Wiza...

Also, it's in the 1.5.0 file: http://jargon-file.org/archive/jargon-1.5.0.dos.txt


Interesting, it seems to have disappeared between 1.5.0 and 2.2.1!


That is interesting -- I didn't check the 2.x revisions, and it only seems to be in 1.5.0 -- though I didn't try to go through all the intermediate files, simply stopping at a failure to find it in the previous one.


Thanks, we updated the title.


Uh... How was this not obvious from looking at it? Every geek who's put together or taken apart a computer knows the metal frame is grounded, and most geeks have enough basic understanding of electricity to understand you only need one wire for a ground. The switch enables or disables grounding. Since that is literally the only thing it can do, that is what it does.


You're close, but not quite there. The ground plane of the machine was almost certainly grounded either way. But this switch likely introduces a connection to a separate ground, resulting in a ground loop. When you disconnect that loop it's not surprising at all that you would get a bit of a voltage spike in the ground plane, hence the crash.

(I was a power electronics engineer a few years ago, before getting into the web.)


most switches don't have one terminal internally connected to the switch body, which then may or may not be connected to ground (or some other potential) depending on what it is mounted on.


I think we are talking late '60s here. Perhaps we are better off now with accessible electronics.


I agree that it's great to be able to get a SBC for the price of lunch, and that just wasn't possible in the 1970s. But the AI Lab PDP-10s were extremely accessible. I walked right up to them several times, and I was never affiliated with the Lab. (I was an undergrad.) The Lab wasn't exactly open to the public, but they didn't actually keep anyone out either.

The PDP-10 itself was mostly discrete logic, so you could see the components and their interconnections just by looking at them. In addition, DEC published full schematics for most of their products. (I never saw the PDP-10 schematics, but it would be unusual if they weren't available.)

If that wasn't enough, Alan Kotok, the architect, came by TMRC every couple of weeks and was more than happy to expound on any part of the system.

https://en.wikipedia.org/wiki/Alan_Kotok https://en.wikipedia.org/wiki/Tech_Model_Railroad_Club


Haha HN, how did this post get downvotes? The second I read about "a switch needing two wires" I thought "Unless it's grounded." Interesting story, but hardly "magic"


Is it common for one of the switch terminals to be electrically connected to the switch's container? That seems like a dangerous idea?


Common? Hell no! Obvious? Yes.

For a switch to work a circuit must be present. Either a neutral line or a ground it is the only way to send information.

If a functioning switch has only a single wire feeding into it then it must be reaching ground through other means.


> If a functioning switch has only a single wire feeding into it then it must be reaching ground

False dichotomy. You omitted a third option: magic.


I suspected ground potential differences halfway through the article too, but I guess for web "hackers" out there it's equal to magic.




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