Wikipedia:Reference desk/Archives/Computing/2007 September 12

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Computing desk
< September 11 << Aug | September | Oct >> September 13 >
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.

September 12[edit]

Hard drive light/motion[edit]

I have a Lenovo laptop, a few months old. For certain periods of time, I will notice every second or two the harddrive light flashing and the harddrive turning (soft "clicking" sound). It will sometimes last continously for a quite a while, and even when no functions are being performed on the computer, no applications are running, and I'm not typing or inputting anything. Does anyone think this is a cause for concern? Thank you for your help. -- 01:29, 12 September 2007 (UTC)

The S.M.A.R.T. capability on my hardrive indicated it might fail. It finally did today. The sounds coming from it are a scraping and clicking sound like an oldtime '78 record player but with metal on metal scraping. Clem 02:06, 12 September 2007 (UTC)
The drive is very likely heading towards failure. The read head thinks it is out of alignment (it may or may not be). It is trying to get back in alignment. Since it is not a viable option to repair whatever is causing the head to think it is out of alignment, your best option is to back up your data and get a new drive - fast. -- kainaw 02:14, 12 September 2007 (UTC)
I'm the person with the first question...mine is making a light clicking sound, not a heavy scraping sound. Do you think my harddrive is still in danger? Thank you. -- 02:18, 12 September 2007 (UTC)
It could be failing, or there could be some sort of hard drive processes going on that you don't know about (logging by background processes which do not appear as applications in your taskbar; or potentially attempts by your computer to access virtual memory stored on the drive). I would first try getting something that would let you monitor hard drive I/O writes and see if it is actually writing or reading anything when it does that. In any case you should get some sort of external backup drive (a good practice anyway). As for possibility of failure, it can vary. I've seen drives with what I would call "minor" noises eventually fail, and I've seen others that kept on sounding like that for years without problems. At this point it sounds like a rather indefinite symptom, and so it is hard to diagnose not only what is causing it, but any sort of long-term prognosis. -- 04:23, 12 September 2007 (UTC)
Get a backup, now. Even if your drive isn't failing, you'll appreciate having a backup sometime later. Look into SMART tools to see if your drive is giving off failure messages. Look for Microsoft/Sysinternal's Filemon to see if there's actually a program doing some work on the disk. (My wireless card driver, for some reason, hits the drive a LOT.) Finally, it could be normal. Some drives will move the heads around from time to time to prevent wearing a hole in the drive. See Hitachi Deskstar for an example. --Mdwyer 19:30, 12 September 2007 (UTC)
Thanks for all your help. I've already got a few backup options, actually. Do you think harddrives on new laptops are sometimes prone to bad behavior (especially cheaper lines of laptops)? -- 02:14, 13 September 2007 (UTC)
This is just a vague personal recollection — so if anyone can supply actual data on the subject, please do — but I do seem to recall reading claims that hard drive failure rates are indeed double-peaked: they tend to fail either when they're new or when they're old, with a period of higher reliability in between. This at least makes intuitive sense: the drives that happen to be a bit off spec to begin with (but not badly enough to be caught by the manufacturer's testing) would be most likely to fail in fairly short order, whereas those that survive the first few months should have a good chance of surviving for several years until gradual wear starts taking its toll. The good news in this case is that if your drive does fail soon, it's likely to be covered by warranty. The bad news is that the warranty will cover a replacement drive, but not data recovery. So make those backups. —Ilmari Karonen (talk) 15:45, 13 September 2007 (UTC)
Bathtub curve. To the original poster: don't get nervous about every sound your HDD makes, just keep good backups and you'll be fine. -- Diletante 15:56, 13 September 2007 (UTC)
Windows is just weird. I've noted the drive fire itself up from time to time for nothing; I see rhythmic patterns in the task manager cpu usage where the usage rises and falls periodically, all by itself. I remember one time trying to save a word document, it demanded to see a floppy that I had temporarily inserted that AM in regard to a completely different document before it would save. That said, it's always smart to have a backup of your drive. obviously. Gzuckier 21:51, 14 September 2007 (UTC)

Zipped (compressed) folders[edit]

I need information on what happens when files contain large amounts of information are zipped (compressed) for a research project if you could help that would be great..

Thanks Teresa —Preceding unsigned comment added by Tkilpatrick (talkcontribs) 04:50, 12 September 2007 (UTC)

I'm not entirely clear on what you are asking, but you could try Data compression and ZIP (file format) for starters. --jjron 08:30, 12 September 2007 (UTC)

Lossless data compression is also one article I would look. --Do not click me! 19:54, 13 September 2007 (UTC)

change directory to user's home[edit]

In linux/bash there is a command to change directory to the user's home "cd ~" I was wondering if there is a command in windows/cmd.exe which will do the same? – 07:16, 12 September 2007 (UTC)

I don't have much experience with Windows or its limited shell, but you might be able to use some of the predefined variables listed here. Also, in bash it is not necessary to type "cd ~", as "cd" on its own brings you to your home directory by default (Windows might do something similar, try it). Another shortcut worth mentioning is "cd -", which brings you back to the previous directory you were in. --Pekaje 11:14, 12 September 2007 (UTC)
cd \ will bring you back to the drive (i.e. C:\). x42bn6 Talk Mess 15:25, 12 September 2007 (UTC)
A bare 'cd' command under DOS/Windows will just display your current directory. I don't know of a shortcut, but the user's home is stored in a number of environment variables. Run the command "set" to see them. In particular, you might have luck with "cd %USERPROFILE%" or "cd %HOMEPATH%" --Mdwyer 19:23, 12 September 2007 (UTC)
You can also use the set command to, well, set variables. F'rinstance "Set home = %HOMEPATH%" will set the value of new variable HOME to whatever the value of the system variable HOMEPATH is. Then, you can simply "cd home" and it will change to that. Caveats: every version of Windows does this a little differently; in XP if you do this with a command window, then close said window, this also will go away; you'd have to do it again, or set it up as a global startup command. Also, this won't work right if your focus is on another drive letter. - 18:31, 13 September 2007 (UTC)

Need Information About RTMX .O.S.[edit]

Hi ALL, I Am in big trouble! I really don't know what is " RTMX.O.S." so please if you have any information reagarding this then put it here! I will be very very thankful to you!!!-- 09:39, 12 September 2007 (UTC)

RTMX is a Real-time operating system based on OpenBSD. -- JSBillings 13:28, 12 September 2007 (UTC)

Loading device drivers[edit]

How can a user load a device driver without administrator privileges in Windows, without a system administrator doing it for the user or giving them administrator rights? Think outside the box 09:59, 12 September 2007 (UTC)

?? Thousands of virus-writers want the answer to this question. Thousands of security programmers are trying to prevent this from happening. Why do you want to add things to the OS, without the person responsible for the box knowing about it? - 18:35, 13 September 2007 (UTC)

Which version of Microsoft Windows? I believe your answer would have at least something to do with that too. --Do not click me! 19:53, 13 September 2007 (UTC)

Windows NT or XP are the ones. I'm trying to run TrueCrypt but the program returns the error: "In order to load the TrueCrypt driver, you need to be logged into an account with administrator privileges". Think outside the box 11:23, 14 September 2007 (UTC)
Of course you can't load a kernel-mode driver (such as TrueCrypt's) in a non-admin account! If you could every single virus would be exploiting that! --wj32 talk | contribs 11:38, 15 September 2007 (UTC)

Online based revision control software[edit]

I am starting a small project (~1000 lines) with a teammate this semester and I would like to use some sort of revision control for the code we will write. SVN has many nice features but I do not have access to a public server where I could install SVN and create a repository. Are there any web based RCS available? Ideally, I would need to be able to upload, download, merge and compare revisions all from a common web interface. --Jcmaco 12:03, 12 September 2007 (UTC)

I win. Websvn or.. the motherlode --frotht 01:54, 13 September 2007 (UTC)

transitor/logic gate switching energy[edit]

(I've been looking at a model of a processor that would need ~1018 logic gate transistions per second.)

My question is: what is the lowest transistor/logic gate switching energy currently available or likely to be available?, and what about the switching energy at smaller than current feature sizes. Thanks. 12:11, 12 September 2007 (UTC) (I'd like to know how big the power supply would need to be...) 13:06, 12 September 2007 (UTC)

I approached this question like a Fermi problem. See Transistor count for some ballpark transistor numbers in modern processors. Let's say you have a Pentium 4, with some ~50 million gates, clocked at ~2 GHz. That will automatically give you 10^17 transistor switches per second. (But this is using the completely unrealistic notion that every gate switches every clock cycle!) In any case, it gives you a first-pass estimate figure for the power consumption. Your hypothetical processor will need on the order of ten times more power than a Pentium 4 (if you used similarly fabricated transistors). Of course, depending on the complexity of your model, you can start doing more detailed analysis. Nimur 15:57, 12 September 2007 (UTC)
You hit the nail on the head with the backwards engineered pentium problem - I considered that - but noticed the same thing - well at least I've got a (very low) lower bound. I'd be suprised if more than 10% are active on average and probably a lot less.. 16:13, 12 September 2007 (UTC)
I'd work from a different CPU: the Pentium 4 bears little resemblance to any other. Switching energy depends greatly on things like transistor size, switching speed, operating voltage, and the like. Further, a large part of a modern CPU's transistor count is cache memory rather than functional units, and has a totally different energy profile. Find a CPU that's similar to what you're considering and estimate from there. --Carnildo 23:42, 12 September 2007 (UTC)
Maybe a celeron without any L2 cache? --Wirbelwindヴィルヴェルヴィント (talk) 16:20, 13 September 2007 (UTC)
This isn't what I'm asking, these processors have unknown logic gate utilisation - the % of 'clocks' that a given gate will be in use. 14:35, 14 September 2007 (UTC)

Application for ordering lists.[edit]

Is there an application that will re-arrange a list, putting it in alphabetical order, based on the first letter of a line? —Preceding unsigned comment added by (talk) 12:27, 12 September 2007 (UTC)

Whenever I need that, I use sort. Without knowing more context, that's all the help I can provide. Some examples of what your requirements are, and information on your computing environment, would be very helpful. --Pekaje 12:32, 12 September 2007 (UTC)
Alas, I run Windows XP. My list consists of movie titles, formatted as:

Donnie Brasco
Godzilla vs. The Sea Monster
Being John Malkovich
etc. 12:40, 12 September 2007 (UTC)

XP also comes with a command-line sort (windows\system32\sort.exe). Also, all of the standard Unix command-line utilities have XP ports -- see GnuWin32 and Cygwin. -- BenRG 12:46, 12 September 2007 TC)
Perfect, I had no idea that was there. Thanks a lot, BenRG. 13:00, 12 September 2007 (UTC)
The documentation on sort.exe is hereMatt Eason (Talk &#149; Contribs) 13:14, 12 September 2007 (UTC)
You could paste the data into MS Excel and do a sort. If it is CSV (Comma seperated values) you can have excel 'convert' it and sort it appropriately. ny156uk 17:01, 12 September 2007 (UTC)

How much does it cost to develop and make a device[edit]

I want to know how much does it cost to develop a new device from scratch. I read of a company called which came with a device called iT which can be found in their website Apart from them, there are many companies like OLPC and mobilis ( More can be found in 1) I just want to know how much does it cost to develop such devices. 2) What are the costs involved in it 3) More info on that —Preceding unsigned comment added by (talk) 12:56, 12 September 2007 (UTC)

The OLPC machines are about US$150, and they aren't trying to make a profit on them, so that's about what they cost to make. They were trying to make it $100, but couldn't manage it. I don't think the development cost is known, as it was a heavily volunteer-supported effort. Intel's Classmate PC is made for a similar market, but priced higher (around $200, apparently). --Sean 15:14, 12 September 2007 (UTC)


my computer has a hard disk cant boot my machine.when i try to boot my pc a message saying "insert proper boot device then resart" appears.i used a friends hard disk and my machine boots okay.when i place my bad hard disk as a slave it slows my makes my 3.2 operate like a

2.0.what could be wrong with it.the place i bought it have no idea whats wrong with itcause everything looks fine on it,it just wont boot my 2.i recently forgot my administrator and i had to run xp a fresh.i have read sumthin about sam there a way i can deactivate my password if i dont remember it.and what do the sam files do? 3.i recently got some videos and they were so crystal clear.they had hdd written on friend told me the music videos are clear coz they r hdd.whats this hdd in relation to videos. can i explain to my small bro what voip simple language.hope am not asking to many questions —Preceding unsigned comment added by (talk) 14:14, 12 September 2007 (UTC)

1. Your hard disk failing? While I think the boot sector is screwy, your best bet is to use Linux System Rescue CD to get any data off the drive. 2. There are many LiveCDs dedicated to either resetting a Windows password or recovering it. Our article on Security Account Manager discusses what SAM files do. 3. As for the videos, you might be thinking of the term HD, specifically in relation to HD video. 4. Our article on VoIP has everything you need. Splintercellguy 17:18, 12 September 2007 (UTC)

Could you rephrase this part for me? --Do not click me! 19:51, 13 September 2007 (UTC) "it makes my 3.2 operate like a 2.0."


I'm trying to use DRAWPLUS on my computer,but when I go to brushes it tells me that the computer doesn't read SSE. Is it because I have an Athlon or is there some other reason? Can anyone help me with this problem? -- ALAN SAUNDERS —Preceding unsigned comment added by (talk) 18:08, 12 September 2007 (UTC)

The original Athlon (before Athlon XP) processors do not support SSE --Spoon! 18:35, 12 September 2007 (UTC)

.mid files out of tune[edit]

I noticed that when playing .mid files in my Windows Mediaplayer (11) under XP, the pitch isn't right. Normaly the A3 should be 440hz, but when playing the midi files it's tuned way below that (aprox. 410hz), which sounds ugly and makes it hard to play along on my piano. Is there a way I can change this? 19:51, 12 September 2007 (UTC)

I don't know much about this stuff (not as much as you seem to do, anyway) but this isn't something that can be fixed with the built in equalizer? Sorry if I'm way of base, but isn't that what it's for? --Oskar 20:02, 12 September 2007 (UTC)
The equalizer only allows you to change the 'frequency envelope' of the sound. What I mean is tuning the pitch of the built-in wavetable-synthesizer that is used when the WMP plays the midi files. I understand that is not an everyday question, but maybe someone knows the answer. 20:10, 12 September 2007 (UTC)
The same thing happens to me. Either every note of my computer's midi or every key of my piano is exactly one half step different from the other, and I can't quite figure out which it is. --Russoc4 20:32, 12 September 2007 (UTC)
Many early music groups use A = 415 Hz. Maybe your Windows time zone is set to Colossal Baroque. -- BenRG 01:40, 13 September 2007 (UTC)
... That's a joke, right? --Russoc4 01:41, 13 September 2007 (UTC)
It could be possible that the pitch control in the audio manager is on something other than zero (if you even have one). The audio manager is an icon in the taskbar that looks like a speaker (different to volume control) or a blue square with a yellow thing in it. Even if that's not what's causing the problem you may be able to adjust the pitch there Mix Lord 03:23, 13 September 2007 (UTC)
According to equal temperament, one half note is an increase/decrease by a factor 1.059463. So if it is tuned exactly one half note too low, then it should be 440/1.059463=415.3 Hz. I don't know Windows media player, but if it plays midi, then it should be possible to tune up or down at least by half notes (and probably to any tuning you like). If not, ditch it and install a proper program. Actually, BenRG might not be joking. There might be an option to set it too all sorts of tuning, such as non-equally tempered, to play stings and flutes and such properly, but also to play in all sorts of exotic keys. DirkvdM 07:41, 14 September 2007 (UTC)
Thanks for the reactions. I wasn't able to find any way to configure the tuning yet, so I suppose ditching WMP might be the best advise yet. 20:03, 14 September 2007 (UTC)
Search for gmreset.mid (i think). I've had this problem where some midi files would leave the machine in a strange state. 'Playing' gmreset (no sound is generated from the file) would fix those problems. --Mdwyer 23:06, 14 September 2007 (UTC)
That sounds like sort of a panic button, something that 'resets' the instrument when a sound-off message has not come through. If that's what it is, it won't help here. Of course, that shouldn't stop you from trying ... DirkvdM 04:31, 15 September 2007 (UTC)
I'd never heard of a midi panic button before. Neat! I'm under the impression that GMRESET.mid does the same thing, but also more. I'd try it no matter what. --Mdwyer 21:28, 15 September 2007 (UTC)
I guess I should've specified that my problem is not only in WMP, it's all midi output on my laptop. --Russoc4 14:01, 15 September 2007 (UTC)

What is Bluetooth?[edit]

Could someone please explain this to me in plain English. Basically, I want to know what it does and how it works. Isn't it some sort of local area networking?-- 22:56, 12 September 2007 (UTC)

It's like wifi but instead of connecting a computer to a network, it's made to connect a wireless device to your computer. It's designed so that your computer doesn't use half its processing thinking it's a router to an entire network, when it's really just connecting to like 2 devices. So different protocol. --frotht 23:52, 12 September 2007 (UTC)
Saying it's for connecting a wireless device to your computer is a bit misleading. Bluetooth is like WiFi in that it's a wireless communication protocol, and used for two devices (such as phone and bluetooth headset). It generally has a low power consumption, short range, and relatively easy to set up. So in a way, it's like the more familiar USB connection; it makes set up easier, but it has limitations, such as causing USB drives to be slower than internal drives, etc. And bluetooth devices still use radio waves, just like USB still uses electricity. --Wirbelwindヴィルヴェルヴィント (talk) 16:07, 13 September 2007 (UTC)

External USB hard drives[edit]

What are the disadvantages? Are they as fast as internal parallel bus drives? —Preceding unsigned comment added by (talk) 23:31, 12 September 2007 (UTC)

Far, far slower transfer rate. My very high-end model (at $150 for 70GB it'd better be high end) transfers 10GB in approx 20 minutes. No effective difference in read/write.. the usb is the bottleneck. But what do you mean "parallel bus drives"? Serial is not any slower. --frotht 23:50, 12 September 2007 (UTC)
Another disadvantage is that they cost more, especially if you buy the ready to use ones (as opposed to buying a standard internal drive plus a case then building it yourself, which still costs more as you have to buy the case). --jjron 09:26, 13 September 2007 (UTC)
It shouldn't be that slow. I just benchmarked my external USB drive at 24.7 MiB/sec sustained, which is 10 GiB in less than 7 minutes. This isn't a high-end drive, just an ordinary consumer IDE drive in a cheap made-in-china case. -- BenRG 23:05, 13 September 2007 (UTC)


1) If the server doesn't have your public key (or you never created a keypair), will SSH still be secure? Does the client generate the key pair on the fly and send the public key as part of the handshake?

2) How do you set up the SSH server so that it only accepts connections from people whose public keys are on the server? --frotht 23:47, 12 September 2007 (UTC)

For 1, I think you're confusing the Pubkey authentication with the session encryption used by SSH. They're two different things. For 2, you set up the sshd on the remote server to only accept PubKey Authentication, and nothing else. -- JSBillings 01:22, 13 September 2007 (UTC)
I know that your key pair can be used for authentication, but isn't it always used to encrypt your session too? It wouldn't make any sense to use an RSA key pair just for authentication. So does SSH have session encryption separate from that that kicks in if you aren't using pre-generated keys? Or does it just make one up automatically? I used to have sshd set up and when I connected to it with putty, putty asked me if I wanted to accept the server's public key.. so presumably the server and putty both generated a key pair on their own without being asked.. right? --frotht 01:38, 13 September 2007 (UTC)
As far as I can remember, the client's public key is only used for authentication. Client authentication doesn't happen until after the client and server have agreed on the session keys, so the security is unaffected by which authentication mechanism you use. SSH supports shared-secret authentication for the client but not for the server, so the server needs a public key but the client doesn't. -- BenRG 01:58, 13 September 2007 (UTC)
The prompt that you get when connecting to an ssh server for the first time (when the client doesn't recognize the key and wants you to decide whether to believe that the server is who he says he is) - that is about the server's host key, which is generated once when the server is installed, and stored on disk so that it persists for the lifetime of the server. In ssh version 2, this can be an RSA key or a DSA key (ssh1 didn't use DSA). Your client will remember this key, and later if you connect to the same server and it's using a different key you'll get a big warning saying the host key has changed. This is a sign that you're not talking a different server using the same name - possibly an impersonator. All of this happens before the user authentication is even considered. --tcsetattr (talk / contribs) 05:59, 13 September 2007 (UTC)
  • Your key pair is never used for encrypting the session, since public key encryption is many times more computationally expensive than symmetric encryption. The public key crypto is only used for authentication and for exchanging single-use symmetric session keys. --Sean 14:02, 13 September 2007 (UTC)