Wikipedia:Reference desk/Archives/Computing/2008 February 18

From Wikipedia, the free encyclopedia

Computing desk
< February 17 << Jan | February | Mar >> February 19 >
Welcome to the Wikipedia Computing Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.


Contents


[edit] February 18

[edit] Types of computer

How can i find or know more about types of computer?--Stylin99 (talk) 01:44, 18 February 2008 (UTC)

It's not really clear what you mean by that. Please clarify. --98.217.18.109 (talk) 02:35, 18 February 2008 (UTC)
You could start with the computer article. Vespine (talk) 21:52, 18 February 2008 (UTC)

[edit] Accessing second computer

I have a Vista and XP machine on my home Wireless LAN (WiFi). Is there anyway I can access files that are on one computer from my other computer?Acceptable (talk) 02:28, 18 February 2008 (UTC)

Yes, look into how to do file sharing/shared folders in Windows. For Vista: [1], for XP: [2] --98.217.18.109 (talk) 02:37, 18 February 2008 (UTC)
But suppose the files are not in shared folders, is there anyway I can access them? Acceptable (talk) 02:40, 18 February 2008 (UTC)
Well, you could just enable sharing on the folders. Or install an FTP server or something and share them that way. You'll need to actually do something with that other computer in either case. Or if you have RDP set up you could conceivably do it that way. -- Consumed Crustacean (talk) 04:37, 18 February 2008 (UTC)
Yeah, you make them shared folders. You can share entire drives if you want. It's the easiest way to do what you want to do. You can also set them up as network drives, if you wanted to. --98.217.18.109 (talk) 15:46, 18 February 2008 (UTC)

Please heed to the warnings about the dangers of allowing root directory access that the "chatty" Windows likes to give. Unless it is a compelling reason, root directory level access to your hard disk over wifi may not be a good idea. Kushal 20:40, 18 February 2008 (UTC)

Right. I presumed they intended to share it with only one other machine and set it up with passwords and the like, not generally share it. --98.217.18.109 (talk) 22:34, 19 February 2008 (UTC)

[edit] CLI app for determining if a sound file is stereo or mono?

This is something that comes up for me a lot... is there a Unix application (command-line) that can look at a sound file and tell me if it's stereo or mono? I know it's possible because LAME can do it, but it will only tell you once it starts encoding, and I'd like to know before that. —Chowbok ☠ 03:04, 18 February 2008 (UTC)

Maybe something like "SoX -V file.wav /dev/null" would work? If it says 1 channel then it is mono, 2 channels then it is stereo.F (talk) 03:19, 18 February 2008 (UTC)
Thanks, but that doesn't work for what I want. I realize I was unclear. The issue isn't trying to find out how many channels an audio file has, it's that I need something to actually look at the sound and see if the two channels are identical (and hence mono). This mainly comes up with audio CDs, which are always two channels, even if it's a mono recording. Does that make sense? —Chowbok ☠ 03:48, 18 February 2008 (UTC)
XMMS has a voice removal plugin - this removes any sound that is the same on both channels. Might help you. Ariel. (talk) 21:49, 18 February 2008 (UTC)
You could just open it in a sound-editor like Audacity and look at the two different channels and see if they are identical. Should be pretty easy to spot 83.250.192.60 (talk) 23:08, 18 February 2008 (UTC)
Sure, but if I were to do that I could just listen to it and figure it out. I'd really like something that could quickly analyze it from a command-line.—Chowbok ☠ 19:14, 19 February 2008 (UTC)
I don't know if this will work but try using the sox program to add a half cycle phase to one channel, then add that channel to the first (avg command). If you get silence they are the same and canceled out. If that doesn't work, and you're a programmer, or can convince sox to do it, add the xmms sound removal plugin to the sox. Ariel. (talk) 21:53, 19 February 2008 (UTC)

[edit] E-mail address availability

I deleted an account with yahoo today. Then I decided I wanted to create a new account. I tried using the same email address that i just deleted but it said it wasn't available. So my question is.. Does an email address get voided once it is used, or can it be "recycled" for someone else to claim that address later. If so how long until I can choose that same address? —Preceding unsigned comment added by 68.7.130.43 (talk) 06:30, 18 February 2008 (UTC)

Seems obvious to me why it would be a bad idea to allow immediate reuse of a deleted address: they don't want to deliver mail to the wrong person, which is what would happen if an address owned by user X suddenly becomes owned by user Y. Forcing the address to be nonexistent for a while gives senders a chance to notice that the old user is gone and stop trying to send there. I haven't heard of any standard waiting period, but I would hope it's at least a week to allow for delayed-in-transit messages to exhaust their retry schedule. --tcsetattr (talk / contribs) 07:38, 18 February 2008 (UTC)
But there's no overall rule. Distribution of user names is entirely up to the owners of the server. You'd have to ask Yahoo for their policy. APL (talk) 13:46, 18 February 2008 (UTC)
If you wanted the same address, why in heaven's name would you delete the account? (Trust me the FBI and CIA can get to whatever . . . ) —Nricardo (talk) 01:14, 19 February 2008 (UTC)
Going to help.yahoo.com and searching for delete account brings up results like How can I delete my account? which indicate that once an account is deleted it can never be re-activated. --Bavi H (talk) 04:59, 19 February 2008 (UTC)

[edit] Give a Brief Note on Hiriyur Town .

Kindly Give a Brief Note on Hiriyur Town Located in Chitradurga District in Krnataka State with the Respective Map Which is Very Necessary For me To Update Our official Website. —Preceding unsigned comment added by 218.248.68.167 (talk) 09:48, 18 February 2008 (UTC)

We have an article on Hiriyur, except it doesn't have a map as such. --Ouro (blah blah) 14:25, 18 February 2008 (UTC)

[edit] Ubuntu root login

Hello How can i login as root in Ubuntu.thanx —Preceding unsigned comment added by Usmanzia1 (talk • contribs) 10:42, 18 February 2008 (UTC)

You are not supposed to. You can use sudo to run a command with root privileges. From the GUI, you will be prompted for your root password whenever you do an administrative action. They consider it safer this way. -- Meni Rosenfeld (talk) 13:12, 18 February 2008 (UTC)

Login? I have always been taught that logging in as root is one BAD idea. Will sudo work? Kushal 13:14, 18 February 2008 (UTC)

It's a bad idea to log in to GDM as root, but there's nothing wrong with logging in as root in the console. To enable the root account type "sudo passwd" and choose a password for your root account, then log in with "su". :D\=< (talk) 16:30, 18 February 2008 (UTC)
I wasn't about to answer, but now that the cat's out of the bag.... there's nothing that stops you from running sudo su. --Kjoonlee 20:41, 18 February 2008 (UTC)
I just go "sudo -i" when I absolutely need a root-console. I almost never do though, regular ol' sudo works for me. 83.250.192.60 (talk) 22:36, 18 February 2008 (UTC)
I'm not a big fan of sudo.. I'm the only user on this system (so root privs delegation isn't an issue) and it's horrifying to use the same password for root as for my user. Thankfully there's some option (I'd tell you but I'm in windows for some reason right now) you can put in sudoers that requires you to provide the root password for privilege escalation to root, and it works perfectly with sudo and gksudo. :D\=< (talk) 05:50, 19 February 2008 (UTC)

[edit] Apophysis Batch Rendering

Does anyone know how you can turn a number of individual .flame files into one batch for rendering? Ive been saving the flames using the 'save parameters' function and now wish to get the whole lot into one .flame file Thanks for any help. —Preceding unsigned comment added by 82.21.54.17 (talk) 12:20, 18 February 2008 (UTC)

[edit] Mac or Cross-platform OpenGL demos?

I have a Geforce 8800 on my Mac Pro. Are there any OpenGL demos that can show off what the card is capable of? --70.167.58.2 (talk) 16:08, 18 February 2008 (UTC)

http://pouet.net :D\=< (talk) 16:40, 18 February 2008 (UTC)

[edit] linux drivers, root, and X

  1. In linux do drivers run in a special ring or software-enforced security level? Does a process have to be running as root to communicate with drivers?
  2. Is that why X has to run as root? Seems like it should have its own user.
  3. Does a separate component handle the mouse cursor or is that just X being monolithic? :D\=< (talk) 16:39, 18 February 2008 (UTC)
1 With the exception of userpace "drivers" (which aren't really drivers at all) like FUSE plugins, they run in Kernel mode (which is ring0 on Intel). As such they have total access to the system, and certainly you have to trust them implicitly. This is one argument for a microkernel design, as drivers run (largely) in userspace with limited capacity to mess things up (although this is designed generally for reliability and error-resistance than downright security). With regard to communication - where the commication happens through the filesystem (/proc entries, named pipes, dev files) then the filesystem security handles who gets access. For system calls - anyone can make any system call, but the kernel and its drivers check the caller to see if they like it (so it's a per-system-call thing, callee checks). I don't know enough about questions 2 and 3 to give a solid answer, but I think X (the X server itself) only runs as root on regular linux systems is because they spawn XDM/GDM etc. which handles user credentials an makes user login processes - you can certainly kill (at least you could on Solaris and older Linux dists, last time I checked) kill the X server and run a fresh one (as a regular user) yourself. -- Finlay McWalter | Talk 16:59, 18 February 2008 (UTC)
That you can kill and restart the X server as non-root doesn't mean it's not using root privileges. It's quite often installed setuid root, which means it gains root privilege on being run, regardless of who started it. There are alternatives, such as running an X server that does all the work through the kernel framebuffer driver, but those aren't very popular. People have become accustomed to writing graphics drivers within the X server infrastructure, and the kernel drivers tend to be less featureful (barely good enough to support a text console). On the subject of putting more advanced graphics drivers in the kernel, Linus once said something like: "We already have a standard graphics interface that everyone uses, and it's called X". --tcsetattr (talk / contribs) 21:08, 18 February 2008 (UTC)
That's really stupid :( Can't wait for hurd to make sense of things (tick, tock) :D\=< (talk) 04:43, 19 February 2008 (UTC)
2: X was (at least at one time) run as root because rather than having video drivers in the kernel, it called ioperm() to allow it to twiddle certain ports on the video hardware itself from user space. Calling ioperm(), unsurprisingly, required root access. The X process would probably drop root privileges after having done so. 3) The X server itself handles the mouse, although I think in some cases there was hardware acceleration for that. --Sean 17:17, 18 February 2008 (UTC)

[edit] Digital camera "face" feature

My digital camera has a feature called "faces" which is supposed to auto-focus or something on peoples faces. My question is, will it work for cats (or animals generally) or is it just people? Thank you! xxx User:Hyper Girl 17:47, 18 February 2008 (UTC)

Face detection typically only works with human faces. It would be possible to create a cat-recognizing computer program. But as far as I know there is no software capable of recognizing faces in general, across species.
For what it's worth I just bought a new camera last week. If you use the screen as a viewfinder you can watch it moving the focus point around (a white box) whenever a human face is in frame. I had the same thought as you and tried it on a couple of cats with no luck at all. APL (talk) 18:06, 18 February 2008 (UTC)
Yeah, it locks onto peoples faces (interestingly not side portraits though) and highlights them in red, but for cats and dogs it doesn't work. I guess it might work on monkeys or other similar facial features. I'm going to try a few things. I wonder if a face drawn on a balloon would work... xxx User:Hyper Girl 18:18, 18 February 2008 (UTC)
's actually a cool experiment. Tell us how it works out with the balloon. Oh, which model camera is it now (curiosity)? --Ouro (blah blah) 19:00, 18 February 2008 (UTC)
I believe these things just look for 2 eyes, a nose, and maybe a mouth and lock-on to them (hence why it doesn't work in profile). An animal with those features easily seen and with similar ratios will probably set it off too. There are surprisingly few variations between faces from a geometry standpoint, basically everyone follows certain rules. 206.252.74.48 (talk) 19:44, 18 February 2008 (UTC)
The canon ixus cameras have this feature for anyone wondering. I have an Ixus 960IS. I thought it was pretty cool but didn't give it much thought, I assumed it was just looking for eyes but then other animals would work I guess there must be more to it.. When I get home I'm going to see if it works on someone with their eyes closed or wearing sunglasses. Vespine (talk) 21:35, 18 February 2008 (UTC)
Hey everyone! No luck with the balloon I'm afraid. But I did get it to lock onto my cats face, once, when she was sitting upright and the camera was at the same level as her. BTW its a Samsung S1050. xxx User:Hyper Girl 15:44, 19 February 2008 (UTC)
The camera can not look for eyes (as logical concept). It can only look for something that looks like eyes. Cat's eyes look quite different from human eyes. Human eyes have white area around the iris. Did you draw the eyes like that in the ballon? - PauliKL (talk) 23:07, 24 February 2008 (UTC)

[edit] Expert Advisor for MetaTrader 4.0

I would like to know if there are any good Expert Advisors for MetaTrader 4.0. If there is could you please let me know, and if possible can I have a copy or source code of the said Expert Advisor.

Thanks. —Preceding unsigned comment added by 97.100.238.160 (talk) 17:54, 18 February 2008 (UTC)

[edit] remote port forward

I've done port forwarding combined with NAT using a machine sitting between me and the internet, but is it possible to do that using a remote machine? i.e. one that is not between me and the internet? I know I can use ssh, but I want the remote IP to be the real one, not the machine that's doing the port forwarding. If not, maybe some sort of VPN, or PPP? Ariel. (talk) 20:19, 18 February 2008 (UTC)

Wait, some clarification: do you wish that all your internet traffic be rerouted through a third-party server so that it appears that your IP is really that of the third-party computer? That's easy, just use a proxy server. There's lists of them on the internet, but using those isn't all that of a great idea, since there are serious privacy concerns. Use TOR, it's easy to install, and very, very private 83.250.192.60 (talk)
Although, I should say, it's got the speed of continental drift. You ain't gonna be watching youtube-videos with it 83.250.192.60 (talk) 22:43, 18 February 2008 (UTC)
No, the opposite of that. I want connections to that other computer to be forwarded to me, but without hiding the 'from' IP addresses. SSH would do the forwarding, but all the connections will look like they come from the remote computer, not the real IP. Ariel. (talk) 23:11, 18 February 2008 (UTC)
What you are describing is essentially an intercepting proxy server (also called transparent proxies) like ISPs sometimes use, and while I don't know how you'd configure it, there's nothing technically impossible about writing a network driver that would reroute all the packets in that fashion. Note though that if you did this, the internet sites would still see the IP of the proxy, but I suppose you wouldn't mind that. 83.250.192.60 (talk) 23:48, 18 February 2008 (UTC)
I'm not trying to hide my, or anyones IP. I'm behind a firewall, and can't accept incoming connections on some ports, so I want a machine (that I control) that is outside the firewall to redirect the connections it receives on one port to a different port on my machine. SSH can do it, and so can rinetd, but both of those change the 'from' IP to that of the machine they run on, and I'm wondering if there is any way to change that. Ariel. (talk) 00:39, 19 February 2008 (UTC)
When people think that the packet came from you, they will send responses directly to you, not some other machine. --131.215.220.112 (talk) 12:00, 19 February 2008 (UTC)

[edit] Exploding a video-file into individual images

What's the easiest way to export all the frames from a video as a whole bunch of jpegs (without having to spend a years rent on video software)? I tried using VLC and using its Image output module, but all the files looked like crap. Any ideas? 83.250.192.60 (talk) 22:31, 18 February 2008 (UTC)

And, oh yeah, I'm running Ubuntu 83.250.192.60 (talk) 22:38, 18 February 2008 (UTC)
It's normal for individual video frames to have less quality than images that were intended to be viewed as stills. You might think they "look like crap" but try playing the video and pausing it. Does the video paused on a single frame really look better? There should only be a slight difference, caused by the lossy re-encoding to jpeg. (Choosing a lossless image format like PNG could help. JPEG can also be done lossless, but rarely is.) You could try mplayer -vo jpeg or -vo png but I wouldn't be surprised if its output is nearly identical to VLC. --tcsetattr (talk / contribs) 23:12, 18 February 2008 (UTC)
Ahh, perfect! Thank you! I did try changing the format to PNG in VLC, but then it only recorded a single frame in a few (it's not the worlds fastest computer I'm using). And yes, the JPGs really looked like crap, they looked like someone printed them out and peed on them. mplayer prints out all the frames, nice and crisp! Beautiful! 83.250.192.60 (talk) 23:58, 18 February 2008 (UTC)

lol ... jpegs are just like that ... it uses lossy compression. Kushal 03:41, 19 February 2008 (UTC)

Yes, I know! I am not a moron, I know that a jpeg loses information and looks bad when you zoom in! The point was that the images produced were barely recognizable as images, they basically looked like someone had mixed the image with cosmic background radiation before faxing them through a bad line and finally coloring them by hand. mplayer also produced jpegs, and they didn't look bad at all, so obviously they were extra-super bad, I didn't just imagine it. 83.250.192.60 (talk) 05:02, 19 February 2008 (UTC)


If you purchase quicktime pro for £20, you can export as image sequence. Just don't save to your desktop like i did, because you run out of room very quickly >_< Radiofred (talk) 11:56, 19 February 2008 (UTC)

I did not know that there is a Quicktime Pro version for GNU/Linux. Kushal 15:00, 23 February 2008 (UTC)