Wikipedia:Reference desk/Archives/Computing/2008 July 24

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July 24

computer software

how does Wi Fi work ?? Is there a way to connect more than two computers simultaneously through bluetooth ??? nemesiskaka —Preceding unsigned comment added by Nemesiskaka (talk • contribs) 07:40, 24 July 2008 (UTC)

Start at Wi-fi and then Wireless communication and Wireless network. As for a bluetooth network i suspect that there will be some hack/program you can get that allows a network to connect via bluetooth. If you have a bluetooth internet connection and 2 networked computers I suspect it would be relatively simple to allow sharing of that connection - as for creating a network using bluetooth it's not something i've come across, but then i've never really found bluetooth to be very appealing. 194.221.133.226 (talk) 08:03, 24 July 2008 (UTC)

Microsoft native Bluetooth stack allows networking devices over Bluetooth. --grawity 13:51, 24 July 2008 (UTC)

Disk Defragmention (moved from Misc Desk)

I defragmented my F: drive recently, and it took over five hours to do so. Is there any way to speed up the process in the future?? Also, after defragmentation, some of the files got compressed (word documents, pictures and such) and now they are shown in blue (I use Windows XP Professional, SP2). What can I do to decompress them, or at least changthe colour to normal black? Thanks in advance. La Alquimista (talk) 11:36, 24 July 2008 (UTC) 11:04, 24 July 2008 (UTC)

As for the time, it's likely restarting because the disk contents have changed (because some application is still running which writes to the disk periodically). I suggest the following method:

1) Restart the computer.

2) Once you log in, use CONTROL-ALT-DELETE to bring up the Task Manager. Kill every process except Explorer.

3) Run Disk Defragmentation.

4) Once completed, restart the computer to restore the applications you killed.

Also, is the compression causing a problem ? StuRat (talk) 11:19, 24 July 2008 (UTC)

When running defragmenter, kill only processes marked as "Username", where "Username" stands for your username. Do not touch other processes. Compressed files don't take longer to load or defragment than normal files and you can change the color back in Windows Explorer: Tools > Folder Options: View > turn off Show encrpted or compressed NTFS files in color. They probably got compressed because you ran Disk Defragmenter on too low disk free space, which also results in much longer defragmentation. Since you defragmented your hard disk now, the defragmentation won't take as long on this disk as before, but you have to defragment it at least once or twice a month and free up at least 20-25% of disk space (not 15% as the program says) to make it run smoothly. Admiral Norton ^(talk) 11:31, 24 July 2008 (UTC)

Ehh...edit conflict. Yes, that's exactly what I was going to say. If I kill a System Process like svchost.exe, the computer automatically shuts itself down. Thanks for telling me how to revert the colour back to normal. La Alquimista (talk) 11:36, 24 July 2008 (UTC)

I guess that must be a diff in Windows versions. On Windows 98, I can kill everything except Explorer, with no trouble. StuRat (talk) 03:24, 25 July 2008 (UTC)

Killing Explorer just kills the desktop and taskbar in XP, it doesn't do any other damage. Admiral Norton ^(talk) 13:27, 25 July 2008 (UTC)

The best bet is to not kill any process that the username "System" started. Kushal (talk) 15:49, 26 July 2008 (UTC)

But the culprit process could be one of those. For example, it may be doing an automatic backup periodically or could be going online to check for updates (and recording a log of this on the computer). Either of these could cause the defrag to restart, since the disk contents have changed. StuRat (talk) 05:11, 27 July 2008 (UTC)

A new device hampering our privacies

Please kindly answer my question:Recently I have heard that a person in my locality possesses a computer, which is even able to display the live video of a short-ranged area.It can even detect the sound voices of the area. The owner of it even claims that he can even view the interior of any house within the range by using X-Ray vision. But the most amazing feature is that the machine be used without even any Internet Connection. Can their be any such machine? If yes, then how can we check it from hampering our privacies? I'll be ever thankful to anyone who would like to answer me. —Preceding unsigned comment added by 117.201.97.83 (talk) 11:38, 24 July 2008 (UTC)

Umm... I think it's far from probable that someone has something like that, unless they come from Krypton. La Alquimista (talk) 11:41, 24 July 2008 (UTC)

X-rays do not work in the way you just described, so there isn't anything to be concerned about. However, terahertz rays can do this, but there isn't anything to be concerned about as this is very exclusive technology - you can't just go into any shop and buy one (actually, I don't think that anyone can buy one). As for a computer that can be used without an Internet connection, this is a normal feature applicable to most computers. With the video-capturing and sound-recording capabilities, these are also normal features of a many modern computers, useful for chatting with someone over the web, or recording movies and music. Absolutely nothing to be concerned about. Rilak (talk) 12:05, 24 July 2008 (UTC)

This device sounds like the one described. Nimur (talk) 22:27, 28 July 2008 (UTC)

The respective person also claims that he can effectively use the machine so as to disrupt the normal flow of working of any electronic device.Several times did my familier persons in the locality did find that many devices such as PCs,Laptops and ACs get damaged.The owner of the device also is a master hacker as known by us.But the man challenges many times many people that he'll destroy their electronic appliances.Within a small span of time many a devices are totally blocked because of some unknown cause. We think that the person is able to send electrical signals in the form of bytecodes which then disturb the normal functioning of the machine. If our theory is right, then can it be considered to be a cybercrime? Please kindly explain to me if it is possible at all. It is to be made known that even our phones and computers have often been blocked and later we did find out that the OS in the system has been corrupted. —Preceding unsigned comment added by 117.201.97.83 (talk) 12:27, 24 July 2008 (UTC)

As has been said, it is very unlikely that a single individual could purchase or build a device with all of the capabilities that you describe. If the person concerned truly believes that they have such as device, then it is possible that they are delusional. However, if you feel genuinely worried and threatened by their behaviour, then you should discuss this with your local law enforcement officers. Gandalf61 (talk) 13:01, 24 July 2008 (UTC)

Most of what you describe doesn't even make any sense. Reading our article on bytecode may give you an idea why. Rilak (talk) 13:08, 24 July 2008 (UTC)

Your theory about 'bytecodes' is complete nonsense, (sorry) but there is a possibility that someone has put together a HERF gun [1]. However, please consider that electronic devices fail all the time, and computers with viruses behave badly on a regular basis. You may be blaming this person for unrelated coincidences. (This is how witch trials get started.) APL (talk) 13:30, 24 July 2008 (UTC)

Power supply noise (I may have gotten the terms wrong - I'm not a electronics person) can fry computers and electronic appliances. That is why manufacturers of expensive computers recommend a power line filter. There are more rational explainations for computer problems than a "mad scientist"-type guy who lives in an old mansion the hill bent on zapping everyone's PCs with electronic death rays. Rilak (talk) 06:16, 25 July 2008 (UTC)

Downloading & UK law

Now that the 6 largest ISPs in the UK have decided to act with the government in identifying and sending out warning letters (and then what, who knows) to file sharers and downloaders of music (& possibly film too) there is an awful lot in the press about "illegal downloading", but no actual information on how and by which statute law/common law precedent the act of sharing files in this way is illegal in the UK. I had always understood that the charicterisation of this as illegal was more the British Phonographic Institute & others point of view than a clearly accepted fact among lawyers/judges. I realise that computing question desk may not be the best area to raise this but I'd expect there are a few here who're aware of the legal issues involved. By the way there was no info at File sharing and the law other than in relation to EU law & no mention as to whether the EU law has been incorporated into UK law.

Copyright and Related Rights Regulations 2003 -- Finlay McWalter | Talk 12:59, 24 July 2008 (UTC)

But after much Googlage I've been unable to find evidence of anyone being convicted under this for filesharing; someone was convicted, then acquitted on appeal, under the anti-circumvention section (for selling modchips). Until there's a fair body of case law, it's not clear exactly what does (and doesn't) contravene the act. It appears that this act tries to close the "making available" defense used in some cases under the equivalent US law, although this covers making available to "the public", which surely covers some kinds of p2p filesharing but arguably might not for others (e.g. for private networks, encrypted networks with invitations needed). -- Finlay McWalter | Talk 13:15, 24 July 2008 (UTC)

I'm not sure how precise you want us to be.. But obviously file-sharing is not illegal in itself..

There are two obviously illegal activities

1. Filesharing illegal material (I'm fairly certain) that people have been prosecuted many times for this - though this may related to 'possesion and distribution' of illegal material generally.

1a. A special case nowadays is filesharing of material that may be used for illegal acts eg terrorism, etc - the material may not be illegal in itself but you may find yourself in trouble in relation to the perceived motive of sharing that material eg how to blow up things..

2. Copyright. File sharing of copyrighted material - probably what you were asking about. In the UK as far as I know the is no fair use (as such) or very little fair dealing allowed (see later)excuse - (copies for ones personal use are generally ok) - but allowing others (especially en masse) to have access to copyrighted material could get you into trouble. I'm sorry I can't give any legal precedents for this. see Copyright law of the United Kingdom - there is a small amount of 'fair use' allowed.

Basically common sense applies here (UK). Offer other people songs/videos etc to many others (for free) and it's away to prison with you... Charge for that and it's 'rough prison' as well. Obviously don't expect to be made an example of just because you and your 'brother' borrowed each others dvds.. Did any of that tell you more than you already new?87.102.86.73 (talk) 17:53, 24 July 2008 (UTC)

Using computer during a thunderstorm

Is it safe to use a computer during a thunderstorm? Are power surges protector enough to protect, well, a power surge caused by a thunderstorm? Also, what are the chances of this happening?--15:28, 24 July 2008 (UTC)

I see no threat of a computer getting zapped by a thunderstorm. Unless you have a metal mouse and keyboard, it won't conduct and surge protector's will sheild your computer. As for your house getting hit by lightning...don't count on it. --Randoman412 (talk) 16:56, 24 July 2008 (UTC)

Most computers have multiple issues with surge from lightning. There is the obvious - the power cord. Then, there is the network connection: (telephone line, network cable, usb cable, coax cable...) that could be directly connected to an outside line. Finally, there are the less probable but possible areas of weakness: all other devices. For example, your monitor may be plugged directly to the wall and get a strong surge from lightning. That surge could possibly be put on the ground line for the video cable and return to the computer, causing damage to the video device inside the computer. The same goes for a printer. So, you should have everything that is plugged into your computer going through a surge protector. Also, it must be a surge protector and not a power strip. -- kainaw™ 17:03, 24 July 2008 (UTC)

Surge protector vendors (at least the name brand ones) generally certify against surges induced by lightning, but not against absolutely all lightning strikes. A typical one is rated at around 15,000 amps - some strikes can be much higher than that. The incredible potential of a lightning strike is such that, if it gets into your house through one wire, it can jump around to other wires across a wide air gap - so it can hit a telephone pole outside your house, run into your house down the phone line, jump to the mains wiring in (or near) something like a DSL modem or a fax machine, and from there run to ground through your computer, toaster, etc. Now this is worst case - the chance of a line right next to your house (where your premises are the most attractive route to ground) is very low, and for that strike to be big enough to get past a half-decent surge protector (which protects the phone line as well as the mains power) is much lower still. -- Finlay McWalter | Talk 17:10, 24 July 2008 (UTC)

Hi. Well, if you want to be really safe during a thunderstorm, do not use, touch, or be near anything connected to the electric, water, telephone, or gas lines, or to the outdoors, roof, or windows. The chances of being struck by lightning are rather small, but people have been struck using the phone or while touching or near other electric devices, which of couse have an insulative casing (and telephones run on a rather very low voltage. It might help if you have a corldless keyboard and mouse, but there may be some problems if lightning strikes your computer's electrical system directly, which is far rarer than striking nearby and causing a temporary power outage. Thanks. ~AH1^(TCU) 18:12, 24 July 2008 (UTC)

Also note that just turning off the computer isn't likely to offer much additional protection beyond the surge protector, you'd have to unplug everything and move the plugs far from the outlets to protect the comp from a lightning strike. StuRat (talk) 03:21, 25 July 2008 (UTC)

About 5 years ago I was using my computer during a thunderstorm and an overhead discharge caused the lights to flicker and disconnected and blew my modem. It was under guarantee and the technician was very puzzled and suggested it had been subjected to some sort of power surge. No, I didn't mention the storm because I thought it was maybe irresponsible to have the machine connected during a storm and it may have affected the guarantee conditions. Richard Avery (talk) 08:08, 25 July 2008 (UTC)

Calling java from command line, want to run more commands

Hi all,

I am running a java app from the command line in Win XP. The java app starts up, and I then want to run more commands from the command line without shutting down the app.

Actually, I've created a batch script (.bat file), and the script calls a second script which just runs 'java -jar ...'. I want to get back into my first script and keep calling commands without shutting down the java app, but control never seems to return to the first script.

Any suggestions? Thanks! — Sam 16:17, 24 July 2008 (UTC)

Instead of saying java -jar foo say start java -jar foo. It will run it in another command-prompt-window, however. -- Finlay McWalter | Talk 16:22, 24 July 2008 (UTC)

Why aren't linear feedback shift registers' output the whole contents of the register?

Linear feedback shift registers' output bit seems always to be said to be the binary digit that is shifted out of the register, e.g. here, here and... just about everywhere else I've looked. I am wondering why the contents of the register couldn't be used as the random number?

At first, I thought that using the contents of the register may produce some kind of a pattern because of all the digits gradually drifting in one direction, but I tested it and the numbers seemed random enough in a decimal base. Moreover, there were the same number of positive changes as negative ones in a complete cycle as long as a the correct tap sequence is used, meaning that if you ignored the fact that you can see all the bits being shifted, you'd think that it was random (although if you seed the register with something like 00000000 00000001, the first few numbers look suspicious).

Does anyone know the reason why the contents of the register is never used? It seems an awful waste of computer power to use only the bit that is shifted out.78.146.52.105 (talk) 16:32, 24 July 2008 (UTC)

An LFSR is like a little production line; as it ratchets forward, each bit gets more mangled up by the state of other bits (cf Avalanche effect). The bit at the end of the process is the most mangled up, so that's the thing we've been making. The other bits are less mangled up, and so are less useful. More formally, if you express the value of each bit value for each position in the register, the one at the end has the most complex equation (that is, it's dependent on the largest number of preceding bits); that means that if an attacker knows or can guess some of the input bits, the value of the last (output) bit is the hardest for them to figure out. As you're trying to make the attacker's life as hard as possible, you only use the scariest mangliest bits you can, those being the ones that come off the end of the register. LFSRs are fairly efficient to code in software (and very easy to build in hardware), so performance isn't such a big concern for most applications. -- Finlay McWalter | Talk 16:52, 24 July 2008 (UTC)

Thanks - that answers my question. You said that LFSRs are easy to implement in hardware, which I would agree with, but normal PCs don't have any hardware implementations of LFSRs do they?78.151.120.231 (talk) 09:39, 25 July 2008 (UTC)

No, indeed not. Given the very limited amount of cryptography that the average user needs her PC to do (view the odd DVD, do a very limited amount of ssl it's not cost effective to build any crypto in hardware. -- Finlay McWalter | Talk 15:02, 25 July 2008 (UTC)

LC3 PROGRAMM IN COMPUTER

HOW TO FIND PAGE NO AND OFSET NO HOW TO DO SIMPLE PROGRAM IN ADDITION,SUBSTRACTION. SOLVED QUESTIONS AND ANSWERS FOR INTRODUCTION TO COMPUTER PROGRAM —Preceding unsigned comment added by 122.164.68.213 (talk) 16:40, 24 July 2008 (UTC)

We have an article about the LC-3 system, which includes a link to the related textbook. -- Finlay McWalter | Talk 16:53, 24 July 2008 (UTC)

The 2nd screen

I have an iMac running leopard and i just got this second monitor which my friend doesn't need anymore. I wanted to know if there was some kind of software that could operate this monitor as a second screen. I know how to plug it in to the iMac, i just want to know if there's software that lets me have 2 desktops like that. --Randoman412 (talk) 16:54, 24 July 2008 (UTC)

Google "dual monitors iMac" and it'll tell you how to do it. It isn't a basic function of the iMac but with some software it can probably be made to do it, depending on your video card. See this article for a nice discussion and links to software. --140.247.241.140 (talk) 18:16, 24 July 2008 (UTC)

That program doesn't work with Leopard or my new iMac. --Randoman412 (talk) 22:42, 24 July 2008 (UTC)

Well Google around some more (e.g.). I'm sure there's a way to do it—seems like others have gotten it to work. --98.217.8.46 (talk) 03:10, 25 July 2008 (UTC)

All Aluminum iMacs support dual monitors without hacks. I believe the revision before could too. But G5 iMacs need a software hack for cetain. --69.148.27.146 (talk) 03:21, 28 July 2008 (UTC)

Can a virus infect the Linux OS?

Is there any virus which may infect the Linux OS? We all know it well that Linux can not generally run .exe files. But it can do so if the WINE' application is used. Apart from this, can a worm or trojan infect the Linux OS? If yes, how should we prevent it? —Preceding unsigned comment added by Asim Chatterjee (talk • contribs) 18:23, 24 July 2008 (UTC)

Every operating system has the capability of being infected. The only way to avoid any and all infections is to have an operating system that refuses to allow anybody to run software on it (which would be useless). The main defence is user intelligence. Teach them to avoid installing malware. The second defence is anti-virus software. If you are running WINE for Windows programs - your specific example - they commonly try to manipulate system files which do not exist in the Linux environment. -- kainaw™ 18:32, 24 July 2008 (UTC)

There are a small number of viruses that can live in a linux machine. The article on Linux malware has a list. APL (talk) 20:16, 24 July 2008 (UTC)

Creating audio cd's on Mac OS 10.4

Is it possible to burn audio content to a cd that can play in an average cd player on Mac OS 10.4 using either built in software or freeware. If so, how? 82.32.51.150 (talk) 19:17, 24 July 2008 (UTC)

iTunes will do it; if it works on OS-X like it does on Windows, you just put a blank CD in and iTunes lets you drag sound files from your iTunes collection over to it, then burn the disk. -- Finlay McWalter | Talk 19:27, 24 July 2008 (UTC)

Ok, thanks, I'll give that a try. 82.32.51.150 (talk) 19:39, 24 July 2008 (UTC)

Format

How do I format a CD? In Command Prompt I type:
format D: /FS:FAT32
It says the file system on the CD is RAW and the new one will be FAT32. (Or FAT, it won't let me format it to RAW.) I ok it and it says verifying 626M and then that it cannot format. Volume is write protected. So then I try to use the CACLS command and it says that that command can only be used on a volume using the NTFS file system. I can't delete any files off of the CD either. How do I get around this problem? Thanks, Ζρς ι'β' ^¡hábleme! 19:42, 24 July 2008 (UTC)

In general CDs and other optical media aren't written to like ordinary disks (floppies, hard-disks, flash drives), but must instead be written (generally in one big go) by speciall optical disc authoring software. In some cases it is possible to use additional packet writing software, which kinda lets you treat the optical disk like a normal disk (with some unfortunate limitations). -- Finlay McWalter | Talk 19:53, 24 July 2008 (UTC)

CDs are read-only file systems. You may be thinking of a CD-R disk, which is typically a write-once file system, or a CD-RW which can be written several times. If the disk is a comercialy produced CD or a homemade CD-R then you're probably out of luck, except in special cases data cannot normaly be removed from a CD or CD-R.

However, CDs are cheap. Just copy the files you want onto a new disk.

You can't easily do this at a dos prompt, however. You'll need some CD burning software. Hope this helps. APL (talk) 19:57, 24 July 2008 (UTC)

Alright, well this brings up another question. I have a .ISO Xubuntu file on my computer. If I put a blank CD-R in the CD tray and right-click the .ISO file and choose "Copy image to CD", will Xubuntu then be bootable from the CD to which the ISO file was copied? Thanks, Ζρς ι'β' ^¡hábleme! 20:33, 24 July 2008 (UTC)

No. An ISO is a special file that contains an image of the CD you want to burn. So rather than copying the ISO file to the blank CD, you need to use a special feature of your CD burning program to burn that ISO image to the disk. Most CD burning programs will have a "burn ISO to disk" or similar option. -- Finlay McWalter | Talk 20:39, 24 July 2008 (UTC)

Well, I have an ISO recorder. Do I need a CD burning program too? Ζρς ι'β' ^¡hábleme! 20:50, 24 July 2008 (UTC)

If [this http://isorecorder.alexfeinman.com/isorecorder.htm] is what you're talking about, then yes, that should work. APL (talk) 21:00, 24 July 2008 (UTC)

Yeah, that is what I have. Ζρς ι'β' ^¡hábleme! 21:03, 24 July 2008 (UTC)

So, I have 736 MB of RAM. Is this enough RAM to run Xubuntu 7.1 live? Ζρς ι'β' ^¡hábleme! 01:20, 25 July 2008 (UTC)

That's more than enough for Xubuntu.IIRC the minimum requirement is around 192 MB :) Abhishek (talk) 03:33, 25 July 2008 (UTC)

is it good

is this laptop good seems good to me i might buy it what do you guys think[2] i wont be playing games like crysis maybe spore and sims 3 so i think it is good what about you guys--Raisins9 (talk) 23:11, 24 July 2008 (UTC)

It seems like a pretty good laptop to me, but really, you're asking for opinions here, not facts. If you can tell what exactly you want to do with the computer, you can probably get better answers on whether this laptop will do the trick for you. Generally speaking, though, I'd say you're going to be fine with this. (You could probably run Crysis on this without any real problems, actually; I'm not that familiar with the laptop graphics adapters, but that's a very recent PCI-E model with half a gig of non-integrated memory, so I'd assume it wouldn't be a problem.) -- Captain Disdain (talk) 01:43, 25 July 2008 (UTC)