Wikipedia:Reference desk/Archives/Computing/2010 March 28

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March 28

Programming languages that are executed by a Virtual Machine

Can I have a list of virtual machines that are used to execute programming languages compiled to a bytecode. I'll start to give an example. --Melab±1 ☎ 01:36, 28 March 2010 (UTC)

The .NET Framework's CLR and MSIL - multiple languages
Java Virtual Machine - multiple languages
Low Level Virtual Machine - multiple languages
Parrot virtual machine - Perl and multiple other languages
...

Yes you can : Virtual_machine#List_of_virtual_machine_software APL (talk) 02:13, 28 March 2010 (UTC)

That is not sufficient for me. I'm looking for ones where the source code is compiled to a bytecode form and then executed by a runtime system. I looking for ones where the use of an intermediate language is integral to execution or that use a virtualized instruction set. Also, I'm not looking for ones that are not reimplementations (i.e. the Mono Project). Let me add another. --Melab±1 ☎ 21:25, 28 March 2010 (UTC)

Vx32

Color management in Windows Vista

Can someone provide a simple explanation of how color management works in Windows Vista? Does Windows compensate for the characteristics of the display device to allow colors to be reproduced accurately on the screen? If it does, does it do that for all applications, or just some? If it does the compensation only for some applications, how do you control or tell if Windows is doing the color compensation for a given application? How do you avoid having color compensation done too many times, say being done by the application when the operating system is already doing it? If you have a choice to compensate for the characteristics of the display either by the OS or by the application, is there a preferred choice? Thanks. —Preceding unsigned comment added by 173.49.11.130 (talk) 04:35, 28 March 2010 (UTC)

Hopefully you started with the color management article. Color correction is usually performed by the video device driver, often taking advantage of graphics hardware features. It applies to (almost) everything rendered to the screen, unless an application explicitly resets the graphics mode using a low-level graphics API. Some advanced image processing software might use this approach, which essentially is duplicating and/or overriding the color correction that has already been provided for by the OS. The only way to avoid this is if the software has an option to disable its internal color-correction (I think Adobe Photoshop has such functionality, and an option to disable it). Adobe Gamma used to be installed and would run in the background at all time "re-correcting" your color profile - wreaking all kinds of havoc, if your OS or video driver was already performing color correction. I believe this problem has been fixed in more recent versions.

Vista provided a new color management API, called the Windows Color System. Here's an official white paper from Microsoft: Windows Color System (MS Word .doc), and here is a great article from an enthusiast site, ColorWiki - about Vista's WCS. They present a good overview of key features, and link to a bunch of MSDN and Microsoft TechNet pages with even more information. Nimur (talk) 10:26, 28 March 2010 (UTC)

Thanks. I'd actually read the articles you referred to, and more, but was (and still is) a little confused. In the Devices tab in Vista's Color Management dialog, multiple profiles can be associated with the same display device. There's a checkbox labeled "Use my settings for this device". What does selecting/unselecting the checkbox do? Does unselecting it mean disabling OS/graphics adapter-level color correction? In my case, the checkbox is unselected and the monitor manufacturer's color profile for the monitor is the default profile associated with the device. With that configuration, nothing comes back from the several photo-printing services I use look like the images in GIMP. (The printed pictures typically look too dark - there seems to be a problem with gamma.) Strangely, I think the problem is not limited to pictures heavily processed with GIMP. Even pictures that have gone through only linear operations (auto contrast enhancement) also seem to suffer the same problem. Any clue? --173.49.11.130 (talk) 13:57, 28 March 2010 (UTC)

Vista and newer versions of windows do have a more sophisticated color calibration system than previous versions (allowing for distinct profiles for different input sources, for multiple monitors, and for output devices like printers). However, identifying the source of color/gamma correction, and actually doing something about it are two different things. Do you have a colorimeter and calibration software to create a calibration profile? If you do, go back over the instructions and be sure to pick an appropriate Gamma level target. If not, I suggest you strive to undo any changes you made to the calibration (i.e. loading anything but the default profile) and reset all of the internal settings on your LCD. If the prints look too dark, it could be simply that your display is overdriving the input causing you to excessively adjust the pictures down. Many LCD panels have different, but equally obtuse options like "magicbright" or "supercolor" in an effort to make the image "pop"... make sure any of this rubbish is turned off. --144.191.148.3 (talk) 14:24, 29 March 2010 (UTC)

Connecting to my ISP

Shall much appreciate some guidance... I have two iMacs, one running Leopard, the other Tiger. Both connect to the internet via ethernet D-Link ASDL modems. The Leopard machine connects with Orange (my ISP) as well as Orange lets it (!). But the Tiger machine hunts for a connection but doesn’t find it. Have checked with Apple, and the problem is probably with the line. But the Leopard connects. The Tiger machine is on the end of a long internal connection - some 100 feet, could this make a difference?Froggie34 (talk) 11:01, 28 March 2010 (UTC)

You do know that you can only have one DSL modem on a single phone line? It sounds like you're trying to use 2 at the same time, which won't work. --Phil Holmes (talk) 11:23, 28 March 2010 (UTC)

Yes, thanks, I only operate one computer at a time. Private upstairs, business down. Never on at the same time.Froggie34 (talk) 13:36, 28 March 2010 (UTC)

It is the modem that makes the DSL connection and is connected all the time, whether or not you are actually using a computer through that connection. You should only use one modem at a time. If you want to use the private/upstairs connection, make sure the modem downstairs is powered-off and/or disconnected from the phone line. And if you want to use the business/downstairs connection, make sure the modem upstairs is powered-off and/or disconnected from the phone line. Astronaut (talk) 16:36, 28 March 2010 (UTC)

Yes, thanks. See my answer above. It ain't the modem. I am connected to the Internet but not to the ISP.Froggie34 (talk) 07:52, 29 March 2010 (UTC)

Now I'm puzzled. How are you connected to the internet but not to the ISP? It certainly sounds like you have two modems connected to your one phone line at the same time. Did you at least try temporarily disconnecting the working one from the phone line to see if the non-working one could make a connection? Astronaut (talk) 10:33, 29 March 2010 (UTC)

I just replaced an ADSL modem. Although the one I replaced worked perfectly fine, the replacement would not connect although all indications were correct. Ultimately the ISP revealed that they have the MAC address of the original modem cached, and had to clear that before another would be permitted to connect. Just a possibility. Alfrodull (talk) 20:20, 31 March 2010 (UTC)

How much do tape drives cost?

I have thought about using a tape drive as an alternative, or supplementary, backup method. However I am unsure about how much this would cost. While I have found tapes (with LTO technology) that only cost about 30 € for 200 gigabytes, the actual drives seem prohibitively expensive. Even the cheapest models, advertised by their manufactures as so cheap they'll knock my socks off, cost well over 1000 €, sometimes over 2000 €. Are there tape drives available for us general consumers, not only for big multi-national companies? JIP | Talk 11:47, 28 March 2010 (UTC)

Even neglecting the drive, those tapes are costing you about 15¢/gb; hard drives cost about half that. Every bulk tape system I've seen has drives that cost a bunch, as you've found. And remember that you'll have to buy another tape drive if the original machine is burned, flooded, stolen, or its power supply turns evil and kills everything in the box. And for a business, which can't afford to wait a week while a new tapedrive is delivered and installed, they really need to get two right out of the box if they want two-site redundancy. In my experience, tapes are clumsy, fragile, error-prone, expensive, slow, noisy, bulky, and inconvenient; they haven't kept pace with the insane progress in size (and to a lesser extent performance) that hard drives have made. -- Finlay McWalter • Talk 12:09, 28 March 2010 (UTC)

Yes, you are right about all that. Furthermore, tapes are sequential access only, while hard drives are random access. The only advantages I have seen to tape drives is that when using a remote backup, you only have to transport the tape in order to at least keep the data intact, which is smaller and lighter, and that whereas a physical fault happening in a hard drive during the power-up cycle would destroy the entire drive, such a fault in a tape drive wouldn't destroy the tape. But given the prohibitive cost of the actual tape drives, I think I might be better off using two or more external hard drives, at least one of which is normally kept at my parents' home. I would think that an easy way to ensure the remote drives keep rotated and thus stay up-to-date is to make regular trips where I take one drive from my home to my parents' home, and there, swap that drive with the one that was already there, and take the old one back home. Then once I'm back home, I update the backup on the drive, and on the next trip, I do this all over again. But I need to keep the data on the drive encrypted while it's off-site. How do I go about that? JIP | Talk 12:30, 28 March 2010 (UTC)

I have no experience with it myself, but truecrypt is often recommended for drive encryption. Equisetum (talk) 12:50, 28 March 2010 (UTC)

And I forgot to mention, it's free and open source. Equisetum (talk) 12:51, 28 March 2010 (UTC)

You could also see Comparison of disk encryption software Equisetum (talk) 12:54, 28 March 2010 (UTC)

(S)DLT and LTO tapes are about half the volume of a slim USB disk enclosure, so the size differential isn't a major issue. I've twice had tapes get wound up inside a drive (once an SDLT, once an LTO3) and both required the drive to be replaced (per our service contract); I don't think tapes are any more reliable than disks. For encryption I'd create a Truecrypt volume on the backup disk, rsync into that, and cleanly unmount. But really, if you're talking about personal backups, do you really have tens or hundreds of gb of confidential data? I segregate my personal "fragile" data (financial stuff, emails, correspondence etc.) into a separate folder, that turns out to be small enough to tar and write to a single DVD. DVDs are great for personal backups, as they're so cheap you can write a backup frequently and you don't have to destroy the old backups (so you end up with an archive - if you delete an important file but don't notice for a couple of years, a rotating backup won't help you). The other stuff (photos, videos, and huge swathes of junk) either doesn't get backed up at all or goes into a rarely-updated couple of disks. Encrypted backup gives you a significant problem - where do you keep the encryption key? Remembering a password you use every day is one thing, but remembering a lengthy passphrase that you almost never use is another thing entirely, and an encrypted backup is useless if you can't remember how to decrypt it. -- Finlay McWalter • Talk 12:58, 28 March 2010 (UTC)

I do have tens of gigabytes of data that, while not exactly confidential, is rather personal. It does contain some things I'd rather not let my parents or my employer see. So the only reason to keep the data encrypted is to prevent a casual observer having access to the drive alone from seeing it. I haven't looked very much into TrueCrypt yet, but I would think having a simple, but non-trivial pass phrase that I keep in my personal belongings would be OK. It's not as if the drives contain company secrets or anything. JIP | Talk 19:52, 28 March 2010 (UTC)

Small silent computer - no fan, keyboard, or display

I am interested in the idea of having a small silent computer in my home, principally to save still images from a CCTV security camera(s) for at least 24 hours. The images would be taken about every one or two seconds.

The computer would literally be in a small cupboard and be on all the time. I want something without a fan, as fans make a noise. I do not want a keyboard or a display, although it may be useful to be able to either plug them in from time to time, or get it to communicate with a desktop computer.

As well as mains voltage, 6 volts and 12 volts is available. I would not mind re-using some "old" device or gadget. Can anyone make any serious suggestions about what I could use please? 78.144.250.185 (talk) 12:40, 28 March 2010 (UTC)

Take a look at a SheevaPlug. You might need to put in a large SD card to store the images (mine runs with a TB USB hard drive, but that of course makes some noise when operating). --Stephan Schulz (talk) 13:06, 28 March 2010 (UTC)

Just curious here, but how quiet does it really need to be? In my experience, the toilet can be flushed at night without waking anyone, so surely an old laptop computer running in a cupboard would be more than adaquate for your needs. Used laptops can be obtained from the small ads in the local paper, the local "used technology" shop, companies renewing their assets, or even friends who are upgrading (for example, I already have 2 used PCs from company renewals and I'm getting three old laptops to refurbish next weekend). Most come with operating systems new enough to work with new webcam/CCTV equipment. Astronaut (talk) 16:26, 28 March 2010 (UTC)

I've bought a number of small PCs like this. The most recent was an Acer Veriton (e.g. [1]). I would imagine these would do what you want. --Phil Holmes (talk) 16:41, 28 March 2010 (UTC)

an old mac mini would work wonderfully for this. their fans would be whisper quiet for the kind of thing you want it to do, and you can probably pick one up for a song on eBay. plus, they will fit well in a cupboard. --Ludwigs2 16:46, 28 March 2010 (UTC)

I suggest old laptops for this specifically because they have everything you need: They are small. They are quiet. They have built-in battery backup. Because most are wireless, you don't need to run wires to it. In case of emergency, it is rather easy to grab the laptop and run out the door (unlike a full-size computer). -- kainaw™ 16:49, 28 March 2010 (UTC)

Let's "think outside the box". The reason they provide the ability to hook up a camera to a computer or monitor is for real-time viewing. If you aren't interested in this, which the "no display" part of your Q implies, then there should be cameras which just store a rotating set of pics in a memory card or, better yet, a USB flash drive. You would then remove that card or flash drive and take it to your computer for viewing (the memory card would require some type of interface device). I would expect that somebody makes this type of security camera. One disadvantage would be that a determine thief could bash the camera and destroy the stored images. However, if they don't spot the camera, don't know it stores the images locally, or aren't able to reach it (maybe because it's behind a window), that shouldn't happen. There could also be a unit that sends a wireless signal to a receiver that stores the images, but that's getting closer to what you mentioned. StuRat (talk) 17:26, 28 March 2010 (UTC)

Mass download of Pdfs

What would be the easiest way to automatically download all the pdfs linked from this page http://www.pdfgeni.com/book/nonlinear-time-series-pdf.html to my HD please? Similarly with Google-Scholar. I have WinXP and Firefox. Thanks. 78.144.250.185 (talk) 15:41, 28 March 2010 (UTC)

http://www.downthemall.net/ ¦ Reisio (talk) 17:00, 28 March 2010 (UTC)

My AV reports that there are a trojan horse on that site, i do not know if it is false alarm or not, be careful. 82.209.130.40 (talk) 12:38, 15 June 2010 (UTC)

Graph editor?

I'm looking for some general-purpose software for editing graphs. Not the kind of graphs that Excel puts out, more like Graph (data structure) or Graph (mathematics).

I'd like to be able to draw some arbitrary nodes, and the connections between them, and export them in a way that my own code could parse. That part is easy enough, but in addition to the graph data, I'd also like to be able to tag the nodes (and perhaps the links) with extra data. (A text description field would be adequate here, if it did not have a restrictive length limit.)

While I'd like to hear about any software that does this, my ideal solution would be something opensource that would run identically on both Windows and Linux, have a reasonably nice GUI, and export the graph in some easy-to-parse format.

This strikes me as a tool that would be handy in a number of situations, so I sort of expected that it would exist somewhere out in the opensource universe, but I can't seem to find it.

Any suggestions would be greatly appreciated. Thanks! APL (talk) 20:41, 28 March 2010 (UTC)

Dia sounds like the best match. Inkscape can do it at a push, but it doesn't really do "connections" the way things like Dia do (if you move a node, you need to move the lines to it as well). -- Finlay McWalter • Talk 20:48, 28 March 2010 (UTC)

Another option is OpenOffice.org Draw, which has similar capabilities to Dia, but a slightly different interface (some prefer one and others the other). Microsoft Visio is an excellent non-free diagramming tool, though I am not sure what the output would be like to parse - it was horrible in office 97 (the last version I used), but this may now use an XML format (I don't know if this is just Word though). -- Q Chris (talk) 20:59, 28 March 2010 (UTC)

Dia is great for making diagrams and exporting them as images, but I'm looking for a tool that will let me get at the STRUCTURE of the graph. I want something that will make graphs that I can export, and then load into my own software as (for example) AI decision graphs, Or state machines graphs, or whatever. Thanks, though. APL (talk) 21:29, 28 March 2010 (UTC)

In case I didn't make it clear, then end result I'm looking to achieve is a Graph (data structure) not a diagram. APL (talk) 21:39, 28 March 2010 (UTC)

My favorite is Microsoft Visio. It is very easy to use. You simply drag the nodes onto the art board and then drag the end points of connectors over them and they snap together. Each object you draw also has metadata (e.g., a description, tags, owner, etc.) It can export your drawings in a myriad of formats. You can also link your diagrams to external data sources, such as a database.--Chmod 777 (talk) 21:46, 28 March 2010 (UTC)

Dia's file format is gzipped XML; any decent language should have an XML parser that will chew through it. Looking at a simple example, everything (nodes and lines) is a dia:object, and they are associated with a dia:connection object that takes the id attribute of two dia:objects. Turning that into a nodelist and a vector list seems very straightforward. -- Finlay McWalter • Talk 21:51, 28 March 2010 (UTC)

If he wants to parse XML-like tags, then he can just export it as an SVG file. But it might be easier to populate the diagram from either an Excel spreadsheet or a database. Both of those can be linked to Visio drawings, and his program can connect to the spreadsheet or database interactively.--Chmod 777 (talk) 21:54, 28 March 2010 (UTC)

A-Hah! You're right! I knew there must be an easy way to do this. Once gzipped, DIA files provide all the info I'll need. I didn't realize that DIA offered an easy way to get at this information.

Thanks much for pointing me towards the solution that was under my nose the whole time! APL (talk) 22:24, 28 March 2010 (UTC)

Here's a tool specifically aimed at graph theory: pigale.sourceforge.net 98.226.122.10 (talk) 22:06, 28 March 2010 (UTC)

There is a standard for describing graphs, the name of which I cannot remember but it involves a dot I think. Several pieces of software can understand and do things with data in this standard, such as displaying it. Update: it is DOT language.78.146.84.14 (talk) 20:56, 29 March 2010 (UTC)