Wikipedia:Reference desk/Archives/Computing/2009 October 24

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October 24[edit]

password reset[edit]

My employer (huge worldwide corporation) requires a number of passwords for various things. If I need a password reset, and depending on the system, it can take anywhere from 1 second to 2 hours for one to be reset. Why does this take as much as two hours though? Are these things likely being handled by cron jobs that just go through a queue every X minutes/hours? I would think that it would be fairly easy to have it done immediately. Info you can offer, appreciate it I would. Dismas|(talk) 03:17, 24 October 2009 (UTC)

Your question has a great deal of possible answers, as it depends on multiple factors. There is no standard convention on how password resets have to be handled, and there are literally millions of applications, each with a wide variety of options that can influence their behavior. A second factor is that the infrastructure of the company can cause this behavior. I can give you some global pointers as to why this should take so long, but i cannot give a definite answer. For that you might want to contact the companies IT department.
  1. The first possibility is indeed as you suggested it - the password system might be handling these requests in batches to reduce server load. Its unusual (And in my opinion not practical) but it is not unheard off.
  2. A second option is that there might be a master server tracking the passwords immediately, while slave servers only synchronize ever so often.
  3. .... (100 more options found in custom software)
Just to give you an example of what custom software might do, in college i once had the joy of using a password changing application made in-house by the IT department. Once you chanced the password it could take minutes to days before it changed, with no obvious indicator as to why it took so long. Eventually we learned that the piece of software did little more then sending a message to IT, requesting the change. Based upon personnel availability (Or their interest to actual do something menial) such a request could take ages. Its unlikely to be the reason for your situation, but it shows does show the amount of factors that can influence such a system. Excirial (Contact me,Contribs) 08:42, 24 October 2009 (UTC)
If you're in a predominantly Microsoft environment, tools like Active Directory can be used to synchronize passwords across multiple environments like windows, outlook, vpn access, etc. This should happen quickly; it does in my corporate environment anyway. However if you have complex systems across multiple unix environments, and database applications to update, IT managers might have policies in place not to allow any automated changes to the environment during peak hours; so a password change on an oracle database might go on a queue and an overworked DBA might get it eventually. In your case the above poster might be right; there could be batches that run every two hours or so to replicate passwords and security updates to satellite servers. Glad help I could, master Yoda. Sandman30s (talk) 20:29, 24 October 2009 (UTC)


Hypothetically I have 5,000 pdf documents of around 500KB per file; if I compress them it reduces their size roughly by half. Would there be any difference in speed (both compression and extraction time) and overall saved space once compressed, between compressing them all together in one .zip file, or compressing them each individually so that they each get their own .zip file? —Preceding unsigned comment added by (talk) 12:19, 24 October 2009 (UTC)

There is no difference between the compression used on the files depending on how many files go into the zip. Zip has overhead that will add to the file size, so compressing them into separate files will take more space than compressing them altogether. It depends what kind of data is in the PDFs, if its text or images or already compressed, but handing a 2 gb file wouldn't be so bad. Look at gzip and zip too. CynofGavuf 18:32, 24 October 2009 (UTC)
I imagine that the speed in decompressing one 2GB file vs. 500KB file is probably noticeable. In such a case it would be worth asking whether you are going to access the files individually or in groups (whether it is worth paying the time "cost" in unzipping them all at once, or whether one-at-a-time makes more sense), which is a use question, not a technical one. There are of course in-between solutions, e.g. zip them up in bundles of 300 or so. -- (talk) 18:48, 24 October 2009 (UTC)
You CAN uncompress a single file from a (huge) archive though, so that may not be a problem. --antilivedT | C | G 23:38, 24 October 2009 (UTC)
I don't know the specifics of the ZIP format, but I guess theoretically you would be able to get higher compression when putting all the documents together - a lot more patterns for the compression algorithm to recognize. (Others will have to fill in on this). This might be more important if the pdfs are very similar. Jørgen (talk) 09:23, 26 October 2009 (UTC)

Windows, 32 v 64 bit[edit]

I've recently bought a new desktop which included a voucher for Windows 7. I've decided to buy it, seen as the reviews I've read seem quite positive. I hadn't really been aware about 32 & 64 bit versions of the os and am trying to decide which version to upgrade to. My system specs are as follow-

Intel Core 2 Quad processor

Geforce GT220, DirectX 10 (1024 MB video mem)


I'm using 32 bit Vista and I use the PC for games, internet browsing & watching DVDs mainly. What would be the pros & cons of updating to 64 bit W7?

Thanks- Stanstaple (talk) 14:14, 24 October 2009 (UTC)

You need to find out if you have a 64-bit processor. While it is not impossible to install a 32-bit OS on a 64-bit processor, it generally isn't a good idea. And installing a 64-bit OS on a 32-bit processor is impossible. There is little practical difference between the 64-bit version and the 32-bit version; you should get whichever one matches your processor. J.delanoygabsadds 14:23, 24 October 2009 (UTC)
My system is 64 bit capable according to Performance Information Tools in control panel, but came preinstalled with the 32 bit version of Vista. Would there be any reason to expect improved performance or compatibility issues if I upgraded to 64? Stanstaple (talk) 14:35, 24 October 2009 (UTC)
I don't know personally, but according to Microsoft, a 64-bit OS is better for a large amount of RAM, which makes sense, because a 32-bit architecture can only address 4,294,967,296 () bytes of RAM without using some sort of a special controller. J.delanoygabsadds 14:54, 24 October 2009 (UTC)
Intel Core 2 is a range of 64-bit processors according to our article. --Tango (talk) 15:24, 24 October 2009 (UTC)
As stated above, 32 bit Windows can address 4 Gigs of memory. However, some of that memory is what it uses for mapping other hardware, such as the graphics controller - it's system memory and not user. This means that, depending upon your system config, a Gig or so of your RAM won't be accessible to run applications in. So if you want to use all of your 4 Gig, you will have to go 64 bit. I'm running 64 bit Vista in 6 Gigs and am happy with the stability and performance. 64 bit apps (e.g. Adobe Lightroom) run very well with all that available memory. --Phil Holmes (talk) 15:29, 24 October 2009 (UTC)
I have a similar choice- 32 or 64 bit Windows 7. My problem is with my production laser printer— the company that made it got bought out and 64 bit drivers were never released. If I could ever find a generic Postscript 64-bit driver, I could hack one, but I could never find it for Vista or XP 64. ---— Gadget850 (Ed) talk 17:31, 24 October 2009 (UTC)
Do you know if I'd have any trouble running games on 64? I know I'd have to run a custom install to upgrade to 64 rather than 32 and that it would involve having to reinstall any programs I've loaded. I've downloaded some games from Steam and I haven't looked into the implications of reinstalling these. Are there advantages to compensate for the extra hassle of a custom install? Would the system run faster or more stably? If I'm repeating myself, it's just to clarify what it is that I want to know. (I'm not much of a techie) Thanks again btw Stanstaple (talk) 19:54, 24 October 2009 (UTC)
There is no trouble running games in win7-64. 32 bit games install into a "Program Files (x86)" folder and so far all have been running perfectly well. I had the same dilemma BTW; first I installed 32-bit and then decided I'd rather have my OS see the extra RAM after finding out about the compatibility with 32-bit. The only drawback is that it won't run any of your old 8/16 bit DOS programs any more. There is always dual-boot to XP for any driver issues (I haven't had any driver issues yet) or if you have loads of RAM you can always use vmware or something to run a virtual machine (XP). I would say stick with 64 bit so that you can make use of future software without having to reinstall win7 again. Sandman30s (talk) 20:14, 24 October 2009 (UTC)
From my experience the older DOS based games don't run *that* well under Windows anyway, so you're best off just running them under DOSBox (which works just fine in Windows 7 64-bit, in fact all the DOS based Steam games actually come with a DOSBox wrapper). ZX81 talk 20:25, 24 October 2009 (UTC)
Just to be clear, I'm not talking about old games (though, if I could find a copy of Frontier Elite I'd love to have another go). I was concerned that modern games were configured for 32 and would be upset by *2. So far my interpretation of what youse are saying is that switching won't mess things up irrevocably, but are there advantages to overcome the bother? Put another way- why should I opt for 64 bit W7 as opposed to 32 bit? —Preceding unsigned comment added by Stanstaple (talkcontribs) 20:39, 24 October 2009 (UTC)
Like it says above multiple times, so you can use more RAM (you have 4Gb at the moment of which you can only really use ~3.25Gb maximum) and for future proofing without the hassle of a reinstall as well as the speed/performance/stability benefits from running a 64-bit operating system. Modern games will run just fine, I have a massive list of games with Steam myself and they ran fine on Vista x64 and I've been running Windows 7 x64 since the August release without a problem. The only thing you really need to be concerned with is driver support for your peripherals so just check you can get a 64-bit Vista driver (since Windows 7 can use those). ZX81 talk 20:51, 24 October 2009 (UTC)
Thanks for the specific response. I've read that I'll be able to use more of the RAM- what I don't know is what difference this will make to my experience of using my computer. No one has said that i'd experience any performance improvements (speed, performance, stability) by going 64. I'm not worried about drivers 'cause I only have the very basics connected. My concern is that I've a 5GB limit on downloads per month- I don't want to have to pay /mb rates for games I've already bought (ie to redownload on steam). What's the upside? Stanstaple (talk) 21:23, 24 October 2009 (UTC)
I don't understand why you believe you'll have to redownload games. You won't. Beyond being able to fully use 4GB RAM (or more) large bitaddress aware 32 bit apps can use 4GB themselves whereas they're limited to 2GB with x32 versions of Windows (with 2GB for the kernel, although this can be adjusted). So can 64 bit apps and of course the Windows kernel. In some circumstances it will definitely offer an improvement, particularly in games which are starting to benefit from more then 2GB of RAM (also other things but you didn't describe anything else likely to majorly benefit). Having said that your graphics card is likely to be a major bottleneck for gaming. (Actually if your primary interest is gaming, internet browsing and DVDs, it would have made a lot more sense to go for a dual core and a better graphics card but that's too late now.) Also 64 bit apps may be faster then their 32 bit counterparts (this isn't guaranteed) although are still many apps that lack 64 bit versions (but it's starting to get to the stage where a lot of the important stuff where it may actually make a difference do have 64 bit versions). I can say from using Windows x64 since 2005 (XP, then Vista now Windows 7) that beyond driver issues and the lack of certain apps which need drivers or a very high integration in the early days (e.g. CD mounting tools, disk utilities, virus scanners, firewalls and Acrobat) as well as the occasional 16bit Windows app, I haven't had any real issues using x64. Obviously there's the need for DOSBox as well but that's starting to get to be a necessity with x32 Windows anyway. P.S. How you differentiate 'speed' and 'performance'? P.P.S. Bare in mind drivers can include stufflike mobile phones, printers, scanners, cameras whether or not they are normally connected P.P.P.S. My final opinion is you will find the benefits from Windows 7 x64 significant in the long run, and more then make up for any occasional problem you may have. The benefits of allowing the OS and apps to use more then 2GB and to use the entire 4GB as opposed to whatever is available now is something you're likely to notice. BTW I don't believe you'll even be using 3.25GB currently. Since you have Vista x32 this should be easy to check but I suspect you'll find 3GB will be available at most, probably even less given that you have a 1GB graphics card. Nil Einne (talk) 21:24, 24 October 2009 (UTC)
Just to second what Nil Einne above said, you'll only need to redownload them if you wipe them. Move them to a different drive/external disk or something that won't get wiped and then after reinstalling just download+install the Steam client (~1Mb) to the same location on the disk as it was previously (I don't think the exact location is a requirement, but I do it anyway), then close Steam, delete the new directory and move the original Steam directory back in place. After restarting Steam you may need to do a client update again, but Steam will take care of that itself. It's worked everytime for me for about 15+ reinstalls over the past few years :) ZX81 talk 21:34, 24 October 2009 (UTC)
I'll lay it straight- I didn't think it was easy to backup programs to disk anymore. If you custom install (which you have to if going from 32 to 64), then all previously installed programs are wiped. All I could find was how to make file backups. I assumed, from reading the ms website, that i'd need the original disk to reload apps. Since I don't know how steam works, I thought I might have problems redownloading games I already bought. Stanstaple (talk) 21:51, 24 October 2009 (UTC)
I've actually been using a method similar to that described by ZX81 for a long while as well (2002/3 maybe?). Instead of reinstalling I just run the Steam client perhaps deleting the "ClientRegistry.blob" file first. Obviously this doesn't create the links etc. With Vista and Windows 7 and UAC it's now often necessary to run in admin first time around as well to install the service (surprisingly it doesn't seem to request admin mode which I would have thought a smart thing to do). I've used this to move between computers and even for multiple installs and different accounts (obviously if you are moving to a friends computer and you don't trust that friend you should take more care) and when reinstalling. However there's actually a backup option in the Steam client as well now although this may not keep stuff like the save games and settings. Look under the file menu... This does require the game to be fully updated etc and obviously doesn't help you if you already installed a new OS or whatever Nil Einne (talk) 22:10, 24 October 2009 (UTC)
ZX81's method doesn't always back up save games anyway (some games store it in My Documents, others in other random places), so it's always best to make sure before you wipe it all out. --antilivedT | C | G 23:35, 24 October 2009 (UTC)
Yes sorry, you're right. Whilst Steam itself is fairly self-contained, the Savegames will sometimes put themselves in My Documents or even your User Profile's Application Data/AppData folders. I completely forgot because I always have a copy of both before installing, but yeh if you want your Savegames, make sure you have all these too! ZX81 talk 23:55, 24 October 2009 (UTC)

Thanks for the responses- I'll read over your answers and if something doesn't gel, I'll get back. Cheers- Stanstaple (talk) 20:06, 25 October 2009 (UTC)

Tuned voltage amplifier[edit]

what are the effects of the rectence, capacitance,resistance, in the tuned voltage amplifier , Discuss its results[1] —Preceding unsigned comment added by (talk) 15:44, 24 October 2009 (UTC)

At least try and hide the fact that you are asking us to do your homework for you... "Discuss its results"? Really... --Tango (talk) 18:43, 24 October 2009 (UTC)
Is there an article on tuned voltage amplifier or voltage tuned amplifier? Perhaps you could write one when you find the answers. You don't mean Voltage controlled oscillator do you? Graeme Bartlett (talk) 22:31, 24 October 2009 (UTC)

In python, os.system() has different results from just entering into Command Prompt[edit]

First off, I'm on a windows XP version Version 5.1.2600, and have python version 2.6.2. Here's the command I'm trying to execute in the command prompt:

"C:\Program Files\Vim\vim72\vim" "C:\Documents and Settings\...etc"

Where ...etc is a whole bunch of sub directories leading to a file. When I paste this command directly into the command prompt, it works exactly as intended. However, for some reason, when I try to execute the exact same command within a python program, using os.system(), I get this error:

'C:\Program' is not recognized as an internal or external command,
operable program or batch file.

I know this is not a mix-up on my part with the quote characters or the backslashes in writing the python strings; I've made sure I'm doing both of those correctly. Anyone have any clue why this is happening, and how I can fix it? That would be much appreciated. -- (talk) 16:22, 24 October 2009 (UTC)

I should probably also mention that other commands don't seem have this problem. For example, when I execute "C:\Program Files\Vim\vim72\vim" on its own, it works in both cases. -- (talk) 16:25, 24 October 2009 (UTC)
I don't have windows to test if is still relevant, but you might want to use the subprocess module anyway. Note that you should pass -- as the first argument to vim if you need to make sure a filename doesn't get interpreted as an option (vim +quit vs vim -- +quit). -- (talk) 17:26, 24 October 2009 (UTC)
Thanks! That worked perfectly. -- (talk) 18:05, 24 October 2009 (UTC)

immune attack[edit]

I have download an eductional game immune attack from net .I have played it but not yet completed it. Each time i have to play it from the beginning, its save option does not work ,how can I save this game and play net part of the game. —Preceding unsigned comment added by True path finder (talkcontribs) 17:09, 24 October 2009 (UTC)

What save option? According to [1]
How do I save the game?
Currently your game cannot be saved, however a user can jump to any game level or in-game cinematic by going to the main menu > instructor menu > and entering the password: abc
Nil Einne (talk) 22:14, 24 October 2009 (UTC)


i have a photo which is in jpg and the face has been blacked out or censored by a black mark. is there a way i can remove the black mark to see the face. Which software should i use? —Preceding unsigned comment added by (talk) 22:37, 24 October 2009 (UTC)

No. JPG does have layers JPG does not have layers. So, it is not possible for the the blackout to be on one layer and the rest of the image be on a different layer. Therefore, the actual pixels containing the original face have been permanently changed to now represent black. -- kainaw 00:34, 25 October 2009 (UTC)
(I think you mean, does not have layers.) The only way out is that sometimes JPEGs are saved with "preview" thumbnails (lower res) that can be of previous versions. There are accounts of photos being "uncensored" in this fashion. I'm somewhat fuzzy myself in how this happened but I can recall it happening a few times in internet lore; perhaps someone else can explain how to extract preview metadata from jpegs, if it is possible. --Mr.98 (talk) 02:35, 25 October 2009 (UTC)
For the record though, there have been attacks on mosaic patterns but that usually involves a source image that is highly predictable. (I'm just talking about the image here, not what could be stored in meta data) For example, people using mosaic filters to blank out check routing numbers. Because those numbers are predictable, it would be plausible to reverse that process. In a way, a mosaic, or any kind of blur, is a hash process. If the hash output maintains the entropy then it is theoretically possible to find the original image. Most won't, but they might maintain enough that you could "brute force" a lot of original source images, and then run the process on them, and compare the output. If they matched then you might have a source image resembling the original.
There are some obfuscations that are easy to crack. For instance the swirl obfuscation is easy to reverse. But mosaic loses some information, although the blurring effect itself is an average of the area it blurs, which means that it will have some relationship to the original. Its threshold will determine the entropy that's preserved, and the reversibility.
But even if all of these methods are theoretically reversible, they are probably not practically so. The swirl one is the most obvious, but a total blur, or a large mosaic should obscure most of a photograph (but maybe not something predictable like text). If you want to do it right use a black box. Shadowjams (talk) 08:14, 25 October 2009 (UTC)
    • ^ Schilling Taub:Electronic Circuits, discrete and Integrated