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September 27

check-sum

how do you compute a tcp check-sum? (if possible, i would love python code for it.) thanks, 70.114.254.43 (talk) 00:53, 27 September 2012 (UTC)

If you're referring to the TCP of TCP/IP, there is a section on the checksum in the article Transmission_Control_Protocol#Checksum_computation. Note the algorithm has differences for IPv4 versus IPv6. Googling tcp checksum calculation python gives several results which have example C code (though unfortunately no Python examples), which should be straightforward enough to convert to Python. There are also a number of hits which discuss using Scapy to do the calculation, which is probably the best way of doing it for production (rather than self-enrichment) purposes. (Avoid re-implementing the wheel.) -- 205.175.124.30 (talk) 02:13, 27 September 2012 (UTC)

screen capture

i was wondering how screen capture software works. (i have some programing experience, and some knowledge of computer hardware.) p.s.: why do you have to hit "save page" on here before you get the captcha? thank you, 70.114.254.43 (talk) 00:57, 27 September 2012 (UTC)

For the captcha, they want to verify you are human before saving, so that seems the logical place, although it would be a pain to type a long entry only to find it's rejected because you can't make out the captcha. BTW, once you sign up for a screen name, they stop asking you to identify captchas here. StuRat (talk) 01:12, 27 September 2012 (UTC)

Screen capture software is architecture-specific (i.e., X Windows is different from Microsoft Windows, etc.), but the general principle is always the same: the system has a bitmap somewhere that represents the current contents of the screen, and the software makes a copy of that bitmap, or a portion of it. Looie496 (talk) 01:52, 27 September 2012 (UTC)

Looie496, is the bitmap is on the ram? — Preceding unsigned comment added by 70.114.254.43 (talk) 02:16, 27 September 2012 (UTC)

In X, the only system I'm intimately familiar with, it lives in the computer's memory address space. In X, the entire screen is treated like a single large window, the "root" window. In any system it has to be stored in some sort of fast memory, but theoretically it could, for example, be on a graphics card or elsewhere. Looie496 (talk) 02:48, 27 September 2012 (UTC)

In the most trivial case, the entire displayable area is laid out in memory in a frame buffer in a useful and convenient data format. A "screen shot" simply dumps that memory to file, in a standard image file format. However, in many computer systems, there need not actually be a complete frame buffer for the entire screen, ever. There are many reasons why; the most common reason is that memory is expensive, and frame-buffers are inefficient ways to use precious system resources. Hardware acceleration can enable pixels to go to the display that have never been resident in RAM; or that have been geometrically transposed to a corrected location. For example, on OS X, you may have on-screen representations using Core Image; and per the official documentation, a Core Image data structure "is a recipe for how to produce the image. The image is not yet rendered." Those pictures show up on your display; but the data that represents them is not a pixel bitmap; it may be a CoreImage object (or anything else). On Windows XP, with video hardware acceleration, a video might appear as a green or magenta rectangle when capturing a screen-shot. So, screen capture can have some subtlety! It is usually desirable that the screen-capture software either emulates the display hardware, executes the image data through the display hardware, or mandates that the operating system produce a valid frame buffer. Not every operating system can or will meet this requirement. Nimur (talk) 03:25, 27 September 2012 (UTC)

No, any rendering that's done by the CPU or GPU always targets an in-memory bitmap. Blitting literally copies bytes from one region of memory to another. In a compositing window manager there's a bitmap for each window and a full-screen bitmap (the primary frame buffer), and whenever some part of a window is repainted the corresponding part of the full-screen buffer is rerendered from the new window bitmap. This uses more video memory than traditional window managers that paint directly to the full-screen bitmap. Hardware overlays do bypass the primary frame buffer, but this doesn't save memory either since the corresponding part of the frame buffer still exists, even though it's obscured by the overlay. The point of the overlay is to avoid the time penalty of writing pixels to the buffer and later reading them back. In general, though, you can't avoid that penalty because you can't compute the pixel values just-in-time in raster scan order. You need a buffer. -- BenRG (talk) 05:05, 29 September 2012 (UTC)

BenRG, above I have cited three examples where a framebuffer is not used. I can cite an additional computer system that does not use a frame buffer: the Cyclone II development board, whose DE2 sample development board contains a video output-port. One classroom exercise included with the design and development documentation is a project to build a VGA output port without using RAM. While I'm sure your experience with many computers has led you to believe that a framebuffer is necessary, it's evident that you've worked with a very small subset of all possible types of hardware and software computer systems. Your assertion that pixel values cannot be computed "just-in-time" is patently false; this style of producing pixels "on-demand" for the video output system is not merely possible, it is commonplace in modern hardware, because it can be significantly more efficient in terms of power, energy-consumption, and dollar-value cost. You may continue to make assertions about whatever you believe that CPUs and GPUs "always" do; but I implore you to check your sources again. Even if we consider only those computer-systems whose hardware- and software- specifications are made public or provided as free software, there are many counterexamples to your assertion. Nimur (talk) 17:25, 29 September 2012 (UTC)

I was talking about ordinary consumer video cards. It's possible in principle to do what amounts to on-the-fly raytracing if you have fast enough hardware or a simple enough scene, but that's not how consumer video cards work. As I said, you are correct about the hardware overlay support that's used by a lot of video players and leaves green rectangles in screen captures. But to the extent that you were talking about consumer video cards—and you seemed to be, given the mention of OS X and so on—everything else you said was wrong. See http://www.opengl.org/wiki/Rendering_Pipeline_Overview for example. -- BenRG (talk) 18:46, 30 September 2012 (UTC)

python mode

need python code to compute "mode" (statistical mode). thank you. 70.114.254.43 (talk) 03:40, 27 September 2012 (UTC)

Here's a quick implementation that gets the mode of its command line arguments:

#!/usr/bin/env python

import sys

def mode(iterable):
    """Get the mode of the items in an iterable."""
    return max(iterable, key=iterable.count)

if __name__ == "__main__":
    try:
        print "The mode is %s." % mode(sys.argv[1:])
    except ValueError:
        """max() was passed an empty iterable."""
        pass

You've not stated what you want to happen when there are multiple items sharing the maximum frequency, or when there are no items in the iterable. For this implementation, I'm assuming that you don't care which item from multiple items gets returned, and I'm assuming that on an empty iterable, you want to raise ValueError (as happens by default by virtue of max()). Cdwn (talk) 04:02, 27 September 2012 (UTC)

Also, if you will always be using hashable objects, you can get a performance increase by converting the iterable to a set prior to passing it to max. Cdwn (talk) 04:21, 27 September 2012 (UTC)

If you are using python 2.7 or later (which you probably should be, if possible), then collections.Counter is very useful for this kind of thing (it assumes the values are hashable). The method collections.Counter.most_common(n) returns the n most common elements and their counts. Also, scipy.stats has a mode function - if you are going to be doing lots of numerical work, it's a good idea to familiarise yourself with numpy and scipy. 130.88.99.231 (talk) 14:49, 28 September 2012 (UTC)

Calender

Since installing Mountain Lion on my AppleMac, the Calendar app. does not seem to 'hold' new events/appointments and they are not there when the app is next opened.. Any ideas as to why please? --85.211.199.83 (talk) 08:25, 27 September 2012 (UTC)

DLP technology history

The article about a screen-door effect presents advantages of Digital Light Processing technology and says:

Newer DLP chip designs promise closer spacing of the mirror elements which would reduce this effect

However, it's been said in 2006, and an external link to the info source is obsolete now. Can anybody verify (and support with some reference) if such solution really was considered at the time and if it eventually got to the market?

Please put your answer at Talk:Screen-door effect#How old is 'newer'?.
--CiaPan (talk) 09:44, 27 September 2012 (UTC)

Quantum cloud computing

Will Quantum computers take over Cloud computing?

The layout would be a big Quantum computer that then runs all of the applications at the same time. It's Hyper-threading with Qubits. The big challenge would be to define the Grid network between all the Virtual machines so they could efficiently share data while they are sharing atoms. Hcobb (talk) 13:24, 27 September 2012 (UTC)

We lack a crystal ball. At the moment, quantum computing is in its infancy and does not look like it will be better than "regular" computers at standard computing tasks anytime soon, perhaps never (the engineering difficulties are big, and the types of problems that quantum computers seem like they will be good at are quite specific). The "big challenge" is to get useful quantum computers at all, at this point. --Mr.98 (talk) 13:40, 27 September 2012 (UTC)

No; quantum computers don't work that way. You might enjoy this article by Scott Aaronson (edit: or this one). -- BenRG (talk) 15:31, 27 September 2012 (UTC)

Extracting information of a pdf file with python

How can you tell Python to open a pdf and maybe extract the title (within the document) or index or~text page x? OsmanRF34 (talk) 14:54, 27 September 2012 (UTC)

pyPdf will do this. But it's a fairly thin layer over the often ungainly PDF document tree, so actually extracting stuff from the document can be a bit laborious. -- Finlay McWalterჷTalk 17:11, 27 September 2012 (UTC)

Wait-free allocator for 2 processes

I'm looking for an implementation or description of a wait-free allocator. It will be used by two concurrent processes, with allocating and freeing happening on both processes. I only need fixed-size blocks. I'm having a hard time finding papers that I don't have to buy, and the only good solution I have found so far is for N processes and variably-sized blocks, so it is much more complicated than I suspect this solution will be. My initial thought is to base it on a wait-free queue, but most information I can find is on single-reader/single-writer or N-reader/N-writer. I'm hoping the 2-process limit will simplify things. 209.131.76.183 (talk) 15:40, 27 September 2012 (UTC)

There is a lot of information on oracle's "no-wait" and "willing-to-wait" latches. These are serialization mechanisms that the CPU uses to control shared (process) access to blocks within oracle's SGA (server memory). I suspect you will find really detailed descriptions on the oracle 7 or 8 mechanism as those were the days when latching and latch contention was more of an issue. Sandman30s (talk) 11:15, 28 September 2012 (UTC)

Computer will not start

Yesterday, my computer took ages to start up successfully, and when it did, I had to reinstall due to a DLL being lost. Today, it won't start up again, originally with a series of rapid beeps and now with silence. My guess is the HDD is dying (as I had similar symptoms when another HDD died) and I need to reinstall on another HDD, but I wanted to bring it here to see if there's another, less drastic, solution. —Jeremy v^_^v ^Bori! 16:54, 27 September 2012 (UTC)

You need to understand the beeps; they're imparting information. See Power-on self-test and then track down a manual giving POST diagnostics for your computer's motherboard. (Except for the "now silence" bit, of course. For that you're going to have to figure out what is & isn't powering up, and whether or not you've dislodged a speaker cable. --Tagishsimon (talk) 16:57, 27 September 2012 (UTC)

The beeps are issued by one of two very rudimentary systems which take care of starting up your computer. If only they sound (and there's no text being displayed on the screen) then a very basic thing is wrong with the system - not a corruption in Windows or a bad hard disk. Depending on what the specific beeps mean for your system, as Tagishsimon describes, it's likely to be a defective or unseated CPU or memory module, a disconnected CPU fan, a problem with the power supply (perhaps just its connection to the motherboard, or a failure of the power supply itself), a defect or bad connection in the graphics adatper, or a defect in the motherboard. A PC will boot perfectly fine (to the BIOS screen) even with no disk drives at all attached - so if you're not seeing the BIOS/POST messages on the screen, the problem isn't the disk drive and replacing it won't help. As Tagishsimon says, you need to find out what these specific beeps mean. -- Finlay McWalterჷTalk 17:08, 27 September 2012 (UTC)

Beeps don't necessarily mean anything serious is wrong -- they could just indicate lack of connectivity to the monitor. But the sequence of symptoms here does indicate something serious -- very serious, if it won't even beep now. Looie496 (talk) 17:18, 27 September 2012 (UTC)

Nothing will print to the screen at this point. (For diagnostic purposes, I use the onboard video as opposed to the PCI card I normally use; that way if something goes wrong I'm not completely screwed), and it will not beep at startup now. (before, it was a series of about 15 beeps in three or four seconds). Googling "SiS 661 POST diagnostic" gives me nothing close to a POST diagnostic for a SiS 661 mainboard. —Jeremy v^_^v ^Bori! 17:26, 27 September 2012 (UTC)

So. Two directions. 1. Can you tell what is & isn't powering up (e.g. motherboard lights, PSU fan, disk lights, etc) 2. Unplug & replug (and sanity check) any connectors that can be disconnected & reconnected. If you cannot progress further than no beeps & no monitor action, then you're stuck. --Tagishsimon (talk) 17:32, 27 September 2012 (UTC)

Motherboard lights aren't powering up, and I think (but am unsure) that the disk lights are not powering up. I haven't checked the PSU fan. I also checked all the connections; everything is still seated as far as I can tell (the processor being the only question mark since it's too compact in there for me to remove the processor fan). —Jeremy v^_^v ^Bori! 17:44, 27 September 2012 (UTC)

So, to sum up: there are no signs of life. Concentrate on the PSU. Is there any evidence that it is alive? What does it smell like (burnt components)? Has it pulled a fuse? (You can also do idiot checks: is the electrical socket you're using supplying power; is the power-lead to the computer intact?). --Tagishsimon (talk) 18:27, 27 September 2012 (UTC)

Forgive my lack of expertise, but this sounds like exactly what happened when the power supply on one of my desktops died. Except that for a long time before it did absolutely nothing, it would turn on for a period of about .5 seconds (long enough for the fan to just start up), then it would instantly die. - Purplewowies (talk) 18:37, 27 September 2012 (UTC)

SiS 661 isn't a motherboard model, it's a Northbridge chipset logic model. It's used on motherboards by many manufacturers (Asus, Acer, Lenovo, Gigabyte, etc.). You need to figure out the maker and brand of the motherboard and look that up, because I don't know if all motherboards with that chip will have the same fail codes. This page lets you download the manual for a Gigabyte board with that chipset - if the beep codes are the same, that document has them on p84. -- Finlay McWalterჷTalk 18:34, 27 September 2012 (UTC)

My rig is manufactured by Cisnet and I think the mainboard is an MSI model. I can't recall which one offhand.

And the computer stays on, fans and all, but there is no signs of life otherwise. I don't smell any burning components, and I have no way to tell if it blew a fuse. I know the socket it's using is supplying power, I have an external HD plugged into a power strip on the same socket and it's turning on normally. That said, the mother end of the plug that goes into the computer is quite loose. —Jeremy v^_^v ^Bori! 18:56, 27 September 2012 (UTC)

Exactly which fans are on? Only the one within the PSU, or ones on the motherboard? --Tagishsimon (talk) 18:59, 27 September 2012 (UTC)

The motherboard fans. (I haven't checked the PSU and haven't yet had a chance to as I'm not at home atm.) —Jeremy v^_^v ^Bori! 19:15, 27 September 2012 (UTC)

I have had a chance to doublecheck, and I smell burning components whenever I turn it on. I've sent for a new PSU off of Newegg. —Jeremy v^_^v ^Bori! 23:39, 27 September 2012 (UTC)

Excellent (or not, as it were). At least you have a path forwards. --Tagishsimon (talk) 23:41, 27 September 2012 (UTC)

Unfortunately, opportunities for burning or melting components aren't limited to the power supply. In particular, the power regulator circuits around the CPU socket carry comparatively hefty currents, and if they fail they're prone to smoking. Look at the large capacitors and toroidal inductors near the CPU (see if some look deformed or scorched) and check that both surfaces of the motherboard, again in the area near the CPU, are free of blackening. -- Finlay McWalterჷTalk 13:03, 28 September 2012 (UTC)

My CPU has a massive fan over it and there's little light in the room where it is situated. I'd have a hard time finding blackening on the mainboard, but I did notice nothing else (incl. electrical components on the mainboard itself) seemed to be amiss. —Jeremy v^_^v ^Bori! 18:38, 28 September 2012 (UTC)

Need an Online Reference Map for "Open-Access" Wifi networks listed in Europe, Esp. G.B.

Hi there, I was just trying to find a website that maps the location of Open Access Wifi Networks in Great Britain (without password). I was listening to Members of the FSF advocating open networks for the public based on ordinary people 'opening-up' their home and business networks to make them available for internet users at large. I am sure that such a map would receive a lot of gratitude-payments for allowing this information to be placed in the public domain. Therefore I was just curious if such a website had taken off as the range of some WiFi_N networks can be up to 100 meters these days. Of course I am sure that there are other efforts to-do this in other countries, so if you are able to specify those websites, it would be much appreciated. --Linuxchatter (talk) 17:28, 27 September 2012 (UTC)

It sounds like you're looking for something like WiGLE. Cdwn (talk) 17:56, 27 September 2012 (UTC)

... or FON. Cdwn (talk) 19:48, 27 September 2012 (UTC)

In many areas of the UK, there is no open WiFi. FON requires a password, obtainable on payment of a fee to BT (unless you are already a BT WiFi customer). The usual advice given in the UK is that WiFi should not be left open because of security risks. Dbfirs 06:58, 28 September 2012 (UTC)

Oh, that's true actually. If you buy your own FON device, you get a username/password. I don't think about it any more as its possible to make it completely transparent. Cdwn (talk) 10:53, 28 September 2012 (UTC)

September 28

Graphing Calculator

Does anyone know of a graphing calculator that is cheaper than the TI-83 but can be used for University Calculus I and II courses? Thanks. — Preceding unsigned comment added by 149.152.23.34 (talk) 00:07, 28 September 2012 (UTC)

The requirements of the calculator will depend on the course. The low-level calc classes I took could be done entirely with a basic scientific calculator, just enough to handle the arithmetic and trig side of things. A more advanced calculator such as the TI-89 will have a CAS that is very useful for verifying your work. I recommend e-mailing the professor or asking about it on the first day of class. There is also no reason to get a brand new calculator - they tend to hold up well and a used one should work just fine, so you may be able to save money that way. 209.131.76.183 (talk) 19:34, 28 September 2012 (UTC)

I totally agree with the previous response. Just look around at amazon or ebay or something to maybe get a used one. I wouldn't worry about how "new" it is anyway unless you plan on using it for years. Chances are you only need it for a couple of courses. When I started calculus, I actually got a TI-92 complete with the manual, CD, and the USB cable for like $30 and it looked brand new with no scratches or anything.174.16.229.18 (talk) 23:37, 28 September 2012 (UTC)

Note that free online graphing calculators are available, too, like GCalc 2: [1]. If you can use them on a portable device, then they would even be useful in class. StuRat (talk) 05:44, 29 September 2012 (UTC)

Probably you are not allowed to use anything different than a portable scientific calculator. And it's also better to study with the same calculator that you'll use at the examination day. OsmanRF34 (talk) 15:19, 29 September 2012 (UTC)

Now you can, now you can't (find a server)

I've been having trouble reaching the Internet. When I click on a link, "Server not found" comes up frequently. (These are links found on pages at normal sites.) The error page offers the opportunity to try again, which usually works after as couple of times. If not, I go back to the page I started from and retry. So far, nothing has remained totally inaccessible.

How can the browser fail to find a server, and then a moment later find it? Is there anything I can do? My browser, Firefox version 15.0.1, assures me I have the latest version. --Halcatalyst (talk) 02:10, 28 September 2012 (UTC)

P.S. Sometimes the browser does return the page, but as the text version. --Halcatalyst (talk) 02:15, 28 September 2012 (UTC)

You're probably not seeing a "text version", but a version without CSS, as that failed to load. "Server not found" implies a DNS problem. Perhaps you have no local DNS cache, and your DNS provider is flaky. What is your operating system? Cdwn (talk) 02:40, 28 September 2012 (UTC)

There are actually many things that could cause this problem. You should follow the steps described at http://support.mozilla.org/en-US/kb/server-not-found-connection-problem. Looie496 (talk) 02:43, 28 September 2012 (UTC)

Whilst true, intermittent failure rules out most of those. Cdwn (talk) 03:13, 28 September 2012 (UTC)

First, what is a local DNS cache? Do I have access to it? (My OS is Windows 7).)

I found out another computer in the household is also experiencing this problem. It's a Mac Powerbook OS X 10.5.8, Safari ver. 5.0.6 (5533.22.3). Also, I followed the steps at the Firefox (Mozilla) "server not found" site, which told me that Firefox was not the problem and that I should look for help at the manufacturer site. Microsoft advised me to use the troubleshooter, but it couldn't identify any problem. Any further thoughts? Thanks, --Halcatalyst (talk) 01:52, 29 September 2012 (UTC)

There's a good chance the problem actually lies with your Internet Service Provider. You might try contacting a customer service representative there. Looie496 (talk) 15:56, 29 September 2012 (UTC)

I called and they took ownership of the problem. They have been having outage issues, but I had not seen interruptions this short. --Halcatalyst (talk) 20:24, 30 September 2012 (UTC)

E-mail content - further use

A person sends e-mail content to several co-members of an organisation. Does that content remain his personal property or can it be forwarded by a recipient to others who are not members of that organisation.?

If forwarded, can the new recipient use the content of the original e-mail? — Preceding unsigned comment added by Cestria998 (talk • contribs) 08:17, 28 September 2012 (UTC)

Both of these are legal questions, for which you would need to consult a lawyer. -- Finlay McWalterჷTalk 13:05, 28 September 2012 (UTC)

They are questions about intellectual property law, but I don't think they're necessarily solicitations for legal advice. One can talk about how copyright works in the general, hypothetical situation (with lots of caveats) without giving legal advice for any specific situation, I think. We are not prohibited from discussing any aspect of how the law works, are we? --Mr.98 (talk) 14:04, 28 September 2012 (UTC)

Generally speaking, one's e-mails — like all of one's writings — are automatically copyrighted if you are in a Berne Convention country, assuming you have not already signed some kind of contract that assigns all work-related copyrights to the organization or institution in question. The rules governing further use of those e-mails vary a lot by jurisdiction, though; fair use comes heavily into play in such situations in the United States. In the past, people who have forwarded e-mails to unauthorized parties, or reprinted them publicly, have sometimes been charged with copyright infringement, but the cases in which one hears about this are usually "whistleblower"-style incidents, and in such cases, such use is often found to be fair use. But, as noted, this is fuzzy legal territory and the specifics make a big difference in any actual, real-life case. --Mr.98 (talk) 14:01, 28 September 2012 (UTC)

As Mr.98 says, it might not be your property in the first place. If you are sending the email as a part of your work, most employment contracts (or at last the ones I have signed) explicitly state that anything you create in the course of your work remains the property of your employer. I have always assumed this is to prevent the kind of (imaginary) scenario where a former employee of Apple claims that he invented the iPhone and Apple must therefore pay him a license fee for each iPhone sold; but it could apply to many other things too. Astronaut (talk) 10:02, 29 September 2012 (UTC)

It's not an entirely imaginary scenario. These contracts emerged when big employers realized that there's actually a lot at stake, especially since a number of big inventions of the 20th century came not from the work someone was explicitly assigned to do, but from stuff they did on the side while doing other work. Universities picked up on this in the early 1910s and 1920s, if I recall correctly, because they realized that if they got a cut of every cool thing their employees discovered or created, that would be a very large cut indeed over the long term. These sorts of contract clauses became very very common in the mid-20th century. --Mr.98 (talk) 15:19, 29 September 2012 (UTC)

Live Twitter updates on mobile

I don't use Twitter a great deal, but I do like using it to follow live events. On my PC I use TweetDeck, which automatically adds new tweets to the top of the timeline. Is there something similar for iOS or Android? All the apps I've found so far rely on manual 'pull to refresh' updates, and I'd rather have it update itself so I can have the full second screen experience. If there isn't something, why not? That is, what's stopping me writing something myself - is there some deficiency in the operating systems or Twitter's API that makes this impossible? - Cucumber Mike (talk) 11:17, 28 September 2012 (UTC)

The official Twitter client for Android does what you are asking, unless I've misunderstood. Cdwn (talk) 11:54, 28 September 2012 (UTC)

I'm not sure. Unless I'm missing a setting somewhere, it only delivers updates on a set schedule - at most refreshing every 5 minutes - or requires a manual refresh. When using TweetDeck updates are delivered instantly. If I'm watching a Grand Prix a lot can happen in 5 minutes, and I like to be able to see people's insights as soon as they are written. - Cucumber Mike (talk) 12:14, 28 September 2012 (UTC)

I use UberSocial on my mobile phone where you can set the refresh interval, they warn that setting it to 5 minutes or shorter will drain your battery rapidly. I assume from this that a live, continuously updating client would be highly impractical. Zunaid 17:23, 28 September 2012 (UTC)

Mmm. I take your point, but let's assume that my device is plugged in and charging, so that power consumption is not an issue. What I want is something like the TweetDeck Chrome app - as that's an HTML5 app I had hoped it would be platform-agnostic, but I can't find a way to make it work on iOS. Thanks for the suggestion of UberSocial though. I'll check it out. - Cucumber Mike (talk) 23:32, 28 September 2012 (UTC)

Bash Shell Options

In the Bash shell, set -o allows you to set these options:

allexport        braceexpand     
emacs            errexit         
errtrace         functrace       
hashall          histexpand      
history          ignoreeof       
interactive-comments    
keyword          monitor         
noclobber        noexec          
noglob           nolog           
notify           nounset         
onecmd           physical        
pipefail         posix           
privileged       verbose         
vi               xtrace

while the shopt builtin lets you set these:

cdable_vars      cdspell         
checkhash        checkwinsize    
cmdhist          dotglob         
execfail         expand_aliases  
extdebug         extglob         
extquote         failglob        
force_fignore    gnu_errfmt      
histreedit       histappend      
histverify       hostcomplete    
huponexit        interactive_comments    
lithist          login_shell     
mailwarn         no_empty_cmd_completion 
nocaseglob       nullglob        
progcomp         promptvars      
restricted_shell shift_verbose   
sourcepath       xpg_echo        

Is there any logic behind the division of options into these two categories? Rojomoke (talk) 16:40, 28 September 2012 (UTC)

bash, like all other shells, has many attributes that are the result of legacy and decisions made for backward-compatibility. So, while there are reasons behind the existence of two seemingly redundant commands - "set" and "shopt" - to set shell options, it's certainly debatable whether these reasons are good or necessary. Here's where you should look for justification: the official bash reference, particularly Section 4.3.1 - the Set builtin - and Section 4.3.2 - the Shopt builtin. From the official documentation, the difference is: set is "so complicated that it deserves its own section"... and shopt "allows you to change additional shell optional behavior." Nimur (talk) 17:37, 28 September 2012 (UTC)

September 29

CD and DVD player laptop not working and cause

What is the cause of CD/DVD player not working in the laptop with the disc in it and how can I fix it? — Preceding unsigned comment added by 65.92.151.92 (talk) 00:31, 29 September 2012 (UTC)

There could be many causes, like the CD not lying flat in the tray and getting jammed in, but the first order of business is to get the CD out. Have you tried rebooting ? Some drives also have a tiny hole in the front where you can insert a pin to force it to open. Try that. StuRat (talk) 00:48, 29 September 2012 (UTC)

How to reboot it?--65.95.105.26 (talk) 14:22, 29 September 2012 (UTC)

"Reboot" means to turn it off, wait a minute, then turn it back on. You may need to hold down the power button (on/off button) to turn it off. If even that doesn't work, unplug it and pull the battery out. StuRat (talk) 17:33, 29 September 2012 (UTC)

Camera lens not fully open

See bits of the lens cover in the top right and bottom left

What causes issues such as this? Like this camera, mine often won't retract the lens cover fully when I turn it on, although it happens frequently enough that I know to touch the cover with my finger, and it immediately retracts the rest of the way. Is it perhaps a problem with a motor? The camera that took this picture is a Canon Powershot, as is mine. I've had the camera for about five years (bought it used from a friend), and it's been doing this for perhaps the majority of the time. Nyttend (talk) 00:39, 29 September 2012 (UTC)

I once had a camera that behaved similarly due to sand getting inside the lens cover, causing it to jam when it tried to open. Looie496 (talk) 02:41, 29 September 2012 (UTC)

Where are the math symbols ?

When editing Wikipedia pages, I used to get a list of special characters to choose from below the edit window. I no longer get that list (actually, it seems to pop up only to be covered immediately by a new white bar at the bottom). I do have a list of special characters above the edit window, but that lacks the math symbols. How do I get them now ? StuRat (talk) 08:15, 29 September 2012 (UTC)

For me, in the "new" vector skin (which IIRC actually went public some time ago), they seem to be accessible from the top bar, Special characters > Symbols, etc.. I'm sure we could figure out how to keep them from disappearing below (which is indeed odd :p), etc., if it bothers you that much. As for a decent explanation for why this happened at all, good luck. ¦ Reisio (talk) 15:46, 29 September 2012 (UTC)

Thanks. StuRat (talk) 17:30, 4 October 2012 (UTC)

Compiling GFortran external subroutines

I would like to have a GFortran program call a GFortran external subroutine contained in a separate source code file, and compiled at a later date, than the calling program. Is this possible ? If so, how do I do it ? (My goal is to compile the external subroutine while the main program is running, then call it.) StuRat (talk) 08:19, 29 September 2012 (UTC)

You need to build, and then link to, a shared object: howto. -- Finlay McWalterჷTalk 08:45, 29 September 2012 (UTC)

To achieve your goal of compiling the .so after the calling program, you need to do something like this:

1. Decide upon the API of the shared object, and create and compile a shared object which presents that API. By compiling it you create a .so file, and you fix the ABI.
2. Compile your calling program against that .so. The compiler uses the API/ABI information in the .so to generate the calling code.
3. Later you can change the source for the .so and recompile it. Only as long as the API and ABI both remain the same (the latter should be unchanged as long as you're on the same platform and you don't change the compiler options) the calling code should be able to call the new shared object.

If you can't do step #1 for some (hopefully unlikely reason) you'd have to use dlopen and dlsym, and then you'd be responsible for managing the call stack manually (which is hard). -- Finlay McWalterჷTalk 09:53, 29 September 2012 (UTC)

Thanks. Have any sample GFortran compile statements to go along with your 2nd post ? StuRat (talk) 10:00, 29 September 2012 (UTC)

It's just the same as the first one. All it means is you mustn't (and hopefully can't; I don't know gfortran's name mangling) change the names or signatures of the calls exported by the .so. Just don't do the dlopen thing. -- Finlay McWalterჷTalk 10:05, 29 September 2012 (UTC)

Thanks. StuRat (talk) 17:30, 4 October 2012 (UTC)

Big fish in a small pond

Is there such a thing as a table showing which Wikipedia editors (excluding bots) have made the most edits? And is it possible to refine that data so that it only reflects edits made in article space, not "community"-style interactions on Talk Pages, the Reference Desk, etc? I'm interested to know which editors contribute the most to this encyclopedia, and which of the prolific editors prefer to use it as a place to hang out. 87.112.50.156 (talk) 10:04, 29 September 2012 (UTC)

WP:List of Wikipedians by number of edits. Mitch Ames (talk) 11:01, 29 September 2012 (UTC)

And is it possible to refine that data so that it only reflects edits made in article space, not "community"-style interactions on Talk Pages, the Reference Desk, etc? 87.112.50.156 (talk) 11:54, 29 September 2012 (UTC)

If you could grab those names programmatically, and feed them through this edit counter, it wouldn't be too hard to get that data. But I don't know if anyone's done that already. --Mr.98 (talk) 15:16, 29 September 2012 (UTC)

You would find that some of the editors with the highest edit counts (even in article space) are not necessarily the most useful. ¦ Reisio (talk) 15:49, 29 September 2012 (UTC)

Right. Creating one well-researched 1000-words article is one edit. Pushing your opinion here and there can means hundreds of edits. OsmanRF34 (talk) 22:14, 29 September 2012 (UTC)

Policing vandalism generates lots of edits, without a single new word added to an article. HiLo48 (talk) 00:08, 30 September 2012 (UTC)

Multiple PCs on one home hub

If I have several PCs connected to the same wireless hub, simultaneously using the web, presumably they are all using the same IP address assigned by the hub, so how do responses from websites get directed to the correct PC (or come to that, to the correct window or tab on a particular PC)?--rossb (talk) 08:03, 30 September 2012 (UTC)

If it's IPv4 (which it almost certainly is) then the box (which is much more a router than a mere hub) does Network address translation. -- Finlay McWalterჷTalk 12:35, 29 September 2012 (UTC)

The answer to the second half of your question is that different connections to the same machine are distinguished by a port number. See simple:network port (or the incomprehensible en:port (computer networking)). Since the network address translation article is also incomprehensible, I'll summarize: NAT maps IP address+port combinations on the Internet side to different IP address+port combinations on the private side. Although there's only one Internet IP address, there are 65,535 port numbers so this trick can handle quite a lot of simultaneous connections. -- BenRG (talk) 16:36, 29 September 2012 (UTC)

Many thanks for the explanation (and apologies for not having originally signed my question). Yes I certainly found en:port (computer networking) pretty difficult to follow. As a further refinement of this, am I right in thinking that a browser will connect to a well-known port (maybe 80) on a server, but the ensuing dialogue will different and more specific port numbers? This whole thing could do with being explained better in our articles.--rossb (talk) 08:03, 30 September 2012 (UTC)

The unique identifier of a TCP connection is the local and remote address and port. So when you connect to a web server on port 80, it's distinguished from other connections to that server only by your address+port. In principle a NAT router could reuse the same local port for connections to different remote address+port combos, allowing up to 65,535 simultaneous connections to each remote address+port instead of 65,535 simultaneous connections total. I don't know how many actually do that. -- BenRG (talk) 15:38, 1 October 2012 (UTC)

redirect not appropriate observation

How/why I got to this page.? On the edit talk for the loudness page, a user was also looking for a page for volume sound for a different reason. quote "I went to Volume (sound) to learn about the entomology of the word "volume" in regards to its acoustics-related definition. It redirected me to Loudness."

And is advised to go to the reference desk.

= So may I ask/challenge why volume sound should redirect to loudness.

http://en.wikipedia.org/wiki/Volume_%28sound%29

= Volume in the context of sound as undefined in wikipedia. I would submit that volume sound should have its own page, with links to loudness. Would myself start to describe volume as a local relativistic indication of scale/phenomenon, and confined to the system your in.

I was looking myself for a description of the contrast between using gain vs/or volume in applied audio engineering. I had elsewhere read that "Gain commands are used to control the volume of selected audio data, in decibels" which seemed wrong, so that was the reason.

= The loudness article is all over the place and lacks tightness and focus. For example initially defining loudness as a perceptual phenomenon, then hearing loss (physical phenomenon) then something completely out of place about loudness compensation.

You should put your comments on the talk page of the relevant article(s). Or you can try to improve articles yourself. -- Finlay McWalterჷTalk 13:36, 29 September 2012 (UTC)

You might be interested in the etymology of "volume": The usage was first recorded (though with a rather wider meaning) in Busby's Dictionary of Music in 1801 "Volume, a word applied to the compass of a voice from grave to acute; also to its tone, or power: as when we say, ‘such a performer possesses an extensive or rich volume of voice’. By the late 1800s the word was being used chiefly to mean the power (decibel) output of a voice. It was then a simple step to transfer the meaning to acoustics, with "volume control" being first used in 1927. The original etymology of the size sense dates back to 1530, though it meant the size of a book originally, and Wycliffe used the words "gret volyms of newe lawes" (great volumes of new laws) around 1380, though he meant books of course. Dbfirs 16:17, 29 September 2012 (UTC)

Files and directories: could it be different

Could an OS be organized without a tree-life directory system? It could be a matrix. Or without files? You could put files as entries in a DB? OsmanRF34 (talk) 15:16, 29 September 2012 (UTC)

Filesystems are already internally organised in ways quite unlike how the file tree abstraction makes them appear, with the abstraction built on top of those various underpinnings. Once you get to networked, replicated filesystems, the internals are very dissimilar from file/tree. People have build several database file systems, which work much as you describe, exposing a DB-like API. But often what ends up happening is a POSIX layer gets built on top of that, and the DB underpinnings get rather neglected (as was the case for the Be File System). It seems people either like a file/dir hierarchy, or that its use is so ingrained in them, and their software, that changing to some other paradigm is more difficult than just writing a different FS API. -- Finlay McWalterჷTalk 15:48, 29 September 2012 (UTC)

But, is there an FS API out there (obviously not mainstream) that doesn't organize files in this way? it's easy to imagine different logical and practical different ways of doing it. OsmanRF34 (talk) 15:56, 29 September 2012 (UTC)

Those described at File system#Database file systems, as I linked above; BeFS, Amazon S3, Hadoop, GFS, etc. It seems when it stops natively having a POSIX-FS API, people stop calling it a filesystem and start calling it a "persistent hash table" or "network storage engine". At the risk of tautology, it seems the world considers "file system" and "file/dir tree" to be synonyms. -- Finlay McWalterჷTalk 16:03, 29 September 2012 (UTC)

But are those for a single user on a PC? Can I navigate my own files through their metadata on my PC? I'll simply put all into one big directory (or whatever that be). OsmanRF34 (talk) 16:13, 29 September 2012 (UTC)

It should be noted that while the Apple iPad has a "file system" (in that it is able to store files, and as such must use some system to do so) it doesn't use a classic directory tree structure to do so, or at least doesn't do so from a user perspective. (I don't know anything about iPad programming, so there may be a tree-based directory structure in the API, but apps typically don't expose that to users directly.) Instead, files are stored on a per-application basis, and the application presents them to the user in whatever ad hoc user interface the app creator wishes. (Anything from a simple flat list, to a tag searchable database, to a non-exclusive hierachical layout, to a context sensitive mind-map.) -- 71.35.101.136 (talk) 04:35, 30 September 2012 (UTC)

• I just want to add that in my view the idea of moving away from directories is really misguided. The human mind finds it easy and natural to organize information spatially, so it is helpful for us to be able to think of a file as located at a place; and there is no better structure than hierarchical directories for making that happen. Looie496 (talk) 17:13, 29 September 2012 (UTC)

• Agreed. Consider installing a software application. Doesn't it make sense to put most of the files in a folder and it's sub-folders, to make uninstall simpler, among other things ? StuRat (talk) 17:38, 29 September 2012 (UTC)

In principal agree, but different OS organize files differently. In Linux the files of one application are not all in one directory/folder or sub-directory/foldre of it. bamse (talk) 18:39, 29 September 2012 (UTC)

If this is really just about tags - the same things used to find blog posts, search music collections, and organize emails in gmail - then they can be used exactly like folders. The user can choose to avoid using multiple tags per file; if the files come with pre-existing tags, the user can ignore those. Each file will then appear to be in only one folder. The resulting bland experience is perhaps the problem that Finlay was referring to; you can lead a horse to a database, but you can't make it adopt an efficient workflow. Except for when the horse is browsing through its music collection, for some reason. Then the horse likes to have Slow Ride simultaneously in the Foghat folder, the Fool for the City folder, the rock folder and the 70s folder.

- I guess you can't nest these "folders" to create a tree structure, but that feature sounds simple to add: it just needs a kind of file which, when double-clicked, searches for a particular tag. That would be equivalent to a folder icon.  Card Zero  (talk) 18:11, 29 September 2012 (UTC)

That is done in Unix/Linux systems: there is a tree of directories, but files are linked to directories rather than placed in them. As a result the same file can be found at the same time in multiple places, possibly under different names. --CiaPan (talk) 21:00, 29 September 2012 (UTC)

Or taking it to the extreme, it might not be a tree at all: http://xkcd.com/981/ --Trovatore (talk) 21:25, 29 September 2012 (UTC)

See CP/M#File system for an example of a very simple non-tree file system. My experience of using such a file system on a multiuser machine in the mid-80s was that executables were put in User 0, where they could be run no matter which user area you were logged into. Each user of the machine was given a user number to store their personal files. User 15 was used for games (and occasionally wiped by management).-gadfium 01:38, 30 September 2012 (UTC)

September 30

Preventing websites from displaying annoying Appstore popups to their respective iOS apps

Is there any way to disable the annoying popups to websites' apps for iOS? For example, when viewing Haaretz it prompts you to either download their app or cancel, on each page. (because merely having a mobile website would be too much convenient) My iPad 3 is jailbroken. Eisenikov (talk) 00:49, 30 September 2012 (UTC)

Disabling certain ads

Hello. I recently had some problems with a business that required me to make several visits to its website. The issues were resolved after a lengthy process, which left me with an extremely negative impression of the business, and at this point I would like to put the whole issue behind me. However, because of my frequent visits to the website, I am now confronted with ads for the business on virtually every website I go to. I know it is due to cookies. But I do not want to be reminded of this business every time I go online. What is the process for getting rid of these specific cookies, without losing the ones I want to keep? (If it means anything, my OS is Windows 7 and I use a Chrome browser.) Thank you.    → Michael J Ⓣ Ⓒ Ⓜ 03:15, 30 September 2012 (UTC)

This thread has a number of solutions. ¦ Reisio (talk) 05:34, 30 September 2012 (UTC)

"my OS is Windows 7 and I use a Chrome browser" well there's you're problem. but if you know witch cookie it is, you can just delete it. but i don't know how to do that on chrome. 70.114.254.43 (talk) 03:53, 2 October 2012 (UTC)

Free HTML editor

Can anyone recommend an editor which handles tables? Kittybrewster ☎ 13:49, 30 September 2012 (UTC)

• I've been using KomPoser http://www.kompozer.net for some time and find it adequate. --Halcatalyst (talk) 15:38, 30 September 2012 (UTC)

I find it Krashes Kontinually. Do you find it does too? I use Vista and Firefox. Kittybrewster ☎ 16:23, 30 September 2012 (UTC)

I use Komposer on Mandriva at home and Windows 7 at work and I've never experienced crashes. --TrogWoolley (talk) 18:42, 30 September 2012 (UTC)

Notepad? -- SGBailey (talk) 09:06, 2 October 2012 (UTC)

I assume they want an editor which recognizes HTML syntax, not a plain text editor. StuRat (talk) 09:26, 2 October 2012 (UTC)

my domain being used by a spammer

I'm getting maybe a dozen emails a day reporting delivery failure of emails allegedly from my domain. Here is part of the header of one of the emails:

"Authentication-Results: mx.google.com; spf=neutral (google.com: 117.201.71.216 is neither permitted nor denied by best guess record for domain of 37CE0D0@dendurent.com) smtp.mail=37CE0D0@dendurent.com"

I'm worried that my domain might get blacklisted. What can I do? --Halcatalyst (talk) 15:34, 30 September 2012 (UTC)

Sender Policy Framework is a web standard for declaring which servers are allowed to send email on behalf of a given domain. It is a useful way of telling third parties that your domain is being spoofed. The "spf=neutral" line in the quoted text appears to indicate that SPF has not been set up for your domain. Dragons flight (talk) 22:40, 30 September 2012 (UTC)

In practice, sensible email receiving organisations are used to falsified "sender:" headers (how many spams do you get that appear to come for yahoo or google, or from your own domain or yourself?). Blocking seems to be done instead on an IP basis (Comcast blocks mail from mcwalter.org, presumably because one of the gazillions of other users of my hosting company was a bad lad once long ago). -- Finlay McWalterჷTalk 00:07, 1 October 2012 (UTC)

Playing Star Control II

Inspired by The Ur-Quan Masters, which I never got to work, I went ahead and bought the original Star Control II for MS-DOS and installed it on my Fedora 17 Linux system, to play under DosBox. The game works perfectly under DosBox, so I have no technical problems. So far I have got as far as to contact Commander Hayes at the Earth starbase to tell him I'm going to free Earth from Ur-Quan slavery, destroy an Ilwrath Avenger, which convinced Hayes of my intentions, and find Spathi captain Fwiffo on Pluto and manage to have him join my fleet. But now I'm at a loss at what to do next. I understand Wikipedia is not a game guide, so the question I'm asking is: where do I find a forum where I could ask for help in proceeding in the game? I don't want a complete walkthrough, as that would spoil me. More like an Internet forum or a wiki specifically for Star Control II. JIP | Talk 17:55, 30 September 2012 (UTC)

In the article Star Control II, in the "External links" section at the bottom, there's a link to "The Ultronomicon, a dedicated Star Control wiki". If you follow that link, on their homepage they also have a "Links" link, which takes you to a page with a number of other sites, including at least one forum. Hope that helps. -- 205.175.124.30 (talk) 20:16, 30 September 2012 (UTC)

Microsoft Excel help

Howdy. I'm a total Excel novice who knows nothing about making formulas on spreadsheets. I am currently working on a schedule. Let's say I input a time of 10:37 pm on cell A2. Can I input a formula so that the time advances every 15 minutes for each cell going down? So, 10:52, 11:07, 11:22, and so on. I've been inputting all the times manually but I figure there must be a less cumbersome way of doing it. 75.162.165.53 (talk) 19:50, 30 September 2012 (UTC)

Fill in the first two entries and select both cells. Then click and hold on the dot at the bottom right of the selected area. Drag it down over the cells you want to fill, and they will be automatically completed. Google "excel autofill" for more info.Rojomoke (talk) 20:18, 30 September 2012 (UTC)

Works like a charm. Many, many thanks for your help. 75.162.165.53 (talk) 20:55, 30 September 2012 (UTC)

You can do this for any repeating series. So if you want to number a column with 1-100, for example. Just put in the first couple and then perform the same action as above. Dismas|^(talk) 02:48, 1 October 2012 (UTC)

October 1

Windows XP

From a programmer's point of view, what may be Windows XP used for, in 2012? And in 2017? I think, Win32 API programming and web page compatibility testing (older versions of Internet Explorer). What else?
Microsoft will stop XP support in the near future, and I've got an old installation disk, so I think, I might install it on a virtual machine and download the updates while they're still available. But I want to know whether it's worth the effort. I'm at university and have no idea of what OS/field I will work on when I finish (2017). --151.75.35.148 (talk) 01:53, 1 October 2012 (UTC)

I'd certainly keep a VM of it. I've kept a VM of mine (which Microsoft consider a re-install, of which you have only a small number). Firstly, as you say, keeping the OS around for API compatibility is useful. Secondly, as it won't get newer versions of Internet Explorer, keeping XP around lets you test new websites with old (but still very common) browser. As you've already paid for XP, this is a nice-to-have; serious commercial Windows developers usually have one of the MSDN subscriptions which gets them a (non-production, no support) install for every Microsoft OS, so they don't care so much. Another reason is historical preservation (if you're willing and able to sit on that VM for a lengthy time) - some software and hardware will never run on Vista/7/8 etc., so having XP around will keep that software alive. Anyway, disk space is fantastically cheap, so keeping a VM, even if you never use it, will cost you very little. -- Finlay McWalterჷTalk 02:01, 1 October 2012 (UTC)

I, for one, cannot run my Sims game on my 7 installation (unless I run it ridiculously vanilla: no expansions, no custom content), and XP has been the only one I've tried thus far that has reliably run the full game long-term. So, as a Sims programmer (albeit not a fantastic or prolific one), testing objects in an XP install would allow me to more accurately gauge if an object or a problem with the installation is causing crashing. So if you're programming for something that is more stable on an older operating system like XP, it can be of help. I had a 7 partition and an XP partition (and a Mac OSX Lion partition) until my XP partition went kaput because the 7 patition did something it wasn't supposed to do. - Purplewowies (talk) 02:23, 1 October 2012 (UTC)

Ok. What set of snapshots would you recommend? What software do you recommend that I preserve? There are a lot of combinations useful for testing: if I save each service pack in couple with each IE version, that's 9 combinations, and more if I consider the OS updates and the applications. Also, I don't know what programs (that I may want for testing/programming purposes) are likely not to be downloadable in XP version in the long future. --151.75.35.148 (talk) 02:39, 1 October 2012 (UTC)

External Hard Drive question & Windows XP question

Hello, I own a 3TB external hard drive from Seagate, and my OS is Windows XP on a laptop from 2006. I was in an IRC chat, and I noticed, while the chat was ongoing, the phrase "does support 2.2TB+ drives". In Googling to find what that means, I saw many results mentioning a 2.2TB limit, but I have no idea if the combination of the 3TB I own and the fact that I still run XP will cause problems? If I was going to have problems, would I have had them immediately upon first trying to use it (I haven't), or will my problem come some time in the future, perhaps when I reach 2.2TB of used space (i.e. 0.8TB free)? Thanks for your help! -- Tohler (talk) 03:29, 1 October 2012 (UTC)

Unfortunately, you may not notice anything wrong until you hit the limit. I suggest a test, where you fill the disk drive by copying files repeatedly. StuRat (talk) 03:47, 1 October 2012 (UTC)

You could also take this opportunity to part ways with Windows XP and 32-bit operating systems, both antiquated. ¦ Reisio (talk) 04:43, 1 October 2012 (UTC)

• According to this document, XP won't naturally support a drive that large. The basic problem is that the variables used by the OS to represent partition sizes and address are not large enough to represent the numbers that you get from such a disk. However according to this page, it is possible to install a Seagate utility called DiscWizard that makes the full capacity of the drive available even under XP. Looie496 (talk) 05:56, 1 October 2012 (UTC)

From what I've read about this, the limit is caused by using sector sizes of 512 bytes. However, it is possible to format the drive to something higher like 4096 bytes, and considering this is a 3TB drive it may already be formatted for 4096 bytes sectors. This should increase the limit to 16TB 92.233.64.26 (talk) 20:09, 1 October 2012 (UTC)

Dual boot Windows XP and Windows 7

Another quick question while I'm using the ref desk: I prefer XP over 7. However, I know I'm going to have to upgrade to a modern computer (e.g. 2012+) eventually. Is it possible to keep on using XP on a modern computer that would have 7 installed "from the factory" (Dell)? How would I go about doing this, and would I run into any problems or limits? (I think one of them is the limit on RAM 32-bit systems can use) -- Tohler (talk) 03:35, 1 October 2012 (UTC)

I split this off as a separate Q. StuRat (talk) 03:40, 1 October 2012 (UTC)

Yes, it's possible. You would need to have the install disks for XP, as you probably won't be able to download it from Microsoft at that point. You will also need a mechanism for controlling which version of Windows boots. Here are a couple approaches:

A) A boot manager can be installed which comes up and asks you which one you want, each time you boot. This might be good if you will be constantly switching back and forth.

B) If you install each version of a different hard disk, you can go to setup when you boot up, and switch the boot drive, to pick the hard drive with the desired O/S. This option would be best if you will use one O/S most of the time. StuRat (talk) 03:44, 1 October 2012 (UTC)

In addition to the RAM (really address-space) issue you describe, you will find it increasingly difficult to find XP drivers for modern hardware. They changed the driver model between XP and Vista, so Vista/7/8 drivers won't work in XP. -- Finlay McWalterჷTalk 03:45, 1 October 2012 (UTC)

To clarify, this means that, at some point, new devices (like printers) will no longer work when you boot in XP. However, they will work when you boot in Windows 7 mode. StuRat (talk) 03:49, 1 October 2012 (UTC)

At this point the documentation and tools are available to allow you to make Windows 7 behave exactly like XP basically every way that matters, if that is your concern. http://classicshell.sf.net/ being easily the biggest piece of the puzzle. ¦ Reisio (talk) 04:59, 1 October 2012 (UTC)

Windows 7 has it own boot manager—Windows Boot Manager, which can handle dual booting with Windows XP including booting from different physical drives. Ruslik_Zero 18:51, 1 October 2012 (UTC)

My solution is to run a windows XP virtual computer on my win 7 machine. I use vmware player which is free, just btw. I've actually grown to like windows 7 quite a lot so my xp computer only gets turned on when I'm doing things like programming microcontrollers which only have xp drivers. You could do most things, even play games on sufficiently powerful hardware, but you do take a processor hit from running the virtual machine on top of win 7. But if you are not doing very processor intensive tasks a VM is a great solution, and you can do your processor intensive tasks on win7, which is a better idea anyway since win 7 will have newer drivers and software version and updates. Vespine (talk) 01:53, 2 October 2012 (UTC)

Does that approach suffer a performance hit over running XP directly ? StuRat (talk) 02:25, 2 October 2012 (UTC)

Yes it does StuRat, have another quick look at my reply above ;) Vespine (talk) 03:48, 2 October 2012 (UTC)

Having said that and mentioning the limitations, there are actually several decent BENEFITS to running a virtual machine. For one, you get one (or just a few) files that represent the whole machine, this makes backups a piece of cake. You can also transfer or copy the entire computer VERY easily, literally like copying a few files. you can keep it on a USB key if you like (obviously the performance won't be great) but you can do it. You can also "snapshot" the configuration once you have it built 'just the way you like it' and revert back to the snapshot if/when you have problems, instead of having to do a full reinstall.. Vespine (talk) 03:53, 2 October 2012 (UTC)

Word PDF Export

I have a Word document that I need to export as a PDF, with its text preserved as text in said PDF. But whenever I go through the appropriate steps, the resulting PDF converts the text to raster images. How can I prevent this? I believe this is something to do with the font I am using, as this does not happen to all the fonts on my computer. Pokajanje|Talk 16:24, 1 October 2012 (UTC)

Some fonts are set with font embedding disabled; if Word honours this, then it won't put the font file into the PDF, and would have to either substitute it for another font or rasterise it. -- Finlay McWalterჷTalk 16:44, 1 October 2012 (UTC)

Here's some info about embedding fonts in Word. -- Finlay McWalterჷTalk 17:05, 1 October 2012 (UTC)

Bad UTP cable affecting some things more than others

I've got a UTP cable from a room to the router downstairs. The connection sometimes gets slow, an internet speed test gives 1.62 Mbps download, 2.63 Mbps upload to the closest server (same town). That download speed is one fifth of what I normally get and what I still get on the pc downstairs, so I'm guessing it's the cable. Both pc's are plugged into an old hub before the router btw, so there's an inherent limit regardless of my ADSL speed. Unplugging the one downstairs does not improve the situation. What I really don't understand, is why downloading pdf files is slowed to about 30 kilobyte per second, and why wikipedia pages load slow, mostly waiting for bits.wikimedia.org, after which they often appear with much of the layout missing, I guess because the style sheet(s) didn't load. I presume that doesn't happen to everyone with a connection speed under 1Mbps or maybe 300kbps, so why would a noisy cable cause this? ifconfig didn't show any errors or dropped packets. Ssscienccce (talk) 19:50, 1 October 2012 (UTC)

It's going to depend on how the application handles bad bits. For some applications, like streaming video, an occasional bad bit may not even be noticeable, so can just be ignored. For other applications, one bad bit can be a disaster, so error detection and correction methods must be used. This could result in sending the same data many times, then giving up after a certain number of tries. This could produce slow response time and missing elements. StuRat (talk) 21:21, 1 October 2012 (UTC)

Bad bits will almost never make it to an application using TCP. There are checksums in TCP and the Ethernet level, and the data will get resent if it is bad. As for the unusual connection issues it would be great if you could confirm it is the cable and not the PC by seeing if the downstairs PC has the same issues when taken upstairs. It may also be a failing port on the hub - try just switching which port you are plugged into, or even bypassing the hub altogether for a quick test. 209.131.76.183 (talk) 13:44, 2 October 2012 (UTC)

October 2

What screen resolution is required to not see jaggies ?

I realize there are smoothing methods to try to disguise jaggies, but that's not what I'm asking about here. Suppose you have the worst-case scenario, of a horizontal line one pixel wide, with a one pixel offset in the middle:

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Would there be any resolution where this would appear smooth, or would it become invisible before it appeared smooth ? How about if we make the line thicker ? We could have 2 pixel thickness and 2 pixel offset:

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But, presumably, this would be the same case as before. So, how about a 2 pixel thickness and a one pixel offset:

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Or 3 pixel thickness and one pixel offset, etc. I imagine technologies which produce "fuzzier" pixels (like CRTs) actually result in the first case looking more like the third. Has anyone studied this ? StuRat (talk) 00:42, 2 October 2012 (UTC)

Here is a nice website, Resolution of the Human Eye, quantitatively comparing an eye to several common metrics used to describe cameras. The Air Force Eye Chart, and many similar charts, use parallel lines of various widths and spacings to quantitatively measure human and instrument resolving power. In fact, eye resolution depends on more than just distance: light conditions, subject color and contrast, and physiological state, all affect the resolution; not to mention immense variation from person to person, especially in light of known optical aberrations like myopia, astigmatism, and hundreds of other special names for different-types-of-blurry-vision. So there's no specific singular answer to your question; you can easily estimate your own eye resolution, or use statistical aggregates such as the ones provided in the references and articles I linked. Finally, I'll comment that antialiasing is not merely a method to disguise sampling artifacts. It's a rigorous, mathematically-robust way to more correctly present or reproduce sampled data. Nimur (talk) 01:11, 2 October 2012 (UTC)

I don't think making everything so blurry you can't see the jaggies is really correcting it, just disguising it. Wearing glasses at the wrong prescription can produce the same result. StuRat (talk) 02:21, 2 October 2012 (UTC)

Properly designed antialiasing involves application of a low-pass filter to band-limit the (reconstructed) sampled data. A low-pass filter can be described as a "blurring" filter. Incorrect parameters will result in a low-pass filter with an overly-aggressive cutoff frequency, which is not optimal and the image will appear blurry. Correct parameters will reproduce a signal that is provably, optimally most-similar to the intended input - even closer to the desired signal than the un-antialiased signal. This is studied in great detail; we have many articles on sampling theory and antialiasing. It is unfortunate, but true, that many crude attempts at antialiasing simply result in blurred images; but any algorithm constructed crudely can mangle data; that's not unique to antialiasing. Antialiasing, implemented incorrectly, blurs the image. Quicksort, implemented incorrectly, can produce unsorted lists; but neither error is the fault of the algorithm. Nimur (talk) 02:34, 2 October 2012 (UTC)

Certainly some attempts are better than others. Still, if I want the maximum contrast between "line" and "not line", and still want the above cases to appear smooth, I can really only get that with a high resolution. With a lower resolution, I have to choose one or the other. StuRat (talk) 03:01, 2 October 2012 (UTC)

You may be interested in Subpixel rendering, which achieves a higher effective resolution around edges in order to smooth them. The animated image on the left of the article is a great demonstration. 209.131.76.183 (talk) 13:35, 2 October 2012 (UTC)

python/cmd/ipv6/ect...

i figure i should put this all in one section, but feel free to split it up.

1: how do i tell if my pc hardware is ipv6 compatible, or does it matter? 2: how do i know/make if my router is ipv6 compatible? 3: what all should i do to get ready for the ipv6 switch?

4: i need i list of commands i can use in the command prompt in windows7? (ones that don't have access restrictions that make them unusable.) 5: how do i use the windows7 ftp client (c:/system32/ftp.exe)? (basic)

6: how do i get a list of functions in a given module in python? 7: how do i use the "ftplib" module in python? (basic)

8: i have windows7, a 7.5gB micro-sd with usb adapter, and a 4.5gB mkv file. when i try to copy the mkv file to the micro-sd card, windows gives an error message saying it's to big. any advice? 9: anyone have an alternative method to copy the mkv file to my friends laptop or pc? (i have no cd/dvd/bd burners, and no extra sd cards or usb drives.) — Preceding unsigned comment added by 70.114.254.43 (talk) 03:22, 2 October 2012 (UTC)

1, 2 & 3)I'm sure there will be people who will disagree, but this is precisely the same question as "what do I need to do to be W2k ready?" back in the day and the answer is the same: Don't worry about it. The people who need to worry about it are taking care of it. Some people are really making a mountain out of a mole hill. Sure there's some fairly complex stuff going on in the back end, but most internet users don't need to worry about it. For the vast majority of people, if you pay for an ISP service, it's up to them to continue the service, whatever that takes. I'll let others address the rest. Vespine (talk) 03:43, 2 October 2012 (UTC)

I'll give 8 a crack since it's a pretty easy one. Your card is probably formatted in FAT32, which means no single file can exceed about 4GB. I think you should just be able to format the SD card in NTFS which will enable it to hold larger files. Vespine (talk) 04:58, 2 October 2012 (UTC)

To answer 6, you can use dir(module) to get a list of all objects in its namespace. vars(module) will return a dictionary of everything in the namespace (including builtins), which can be unnecessarily verbose if the creator didn't define __all__. →Σσς. 06:36, 2 October 2012 (UTC)

proxy-server

is there any such thing as a tunneling proxy? one to tunnel ip thru icmp, for example. so if i wanted to send data to a port my firewall blocks, i could trick it. cause i can't use yacy, cause i don't control my firewall. (also, i don't get the capchas when i save edits anymore. i don't know if that's a malfunction or not.) thank you, 70.114.254.43 (talk) 04:09, 2 October 2012 (UTC)

It's very uncommon to use ICMP for anything other than ICMP, because it lacks some pretty important pieces of a reliable internet transport protocol: error-checking and correction, automatic retransmission of lost data; sequencing, and so on. Not to mention, sending malformed or otherwise "irregular" ICMP packets is sure to draw the ire of commonplace automated security software on internet routers, potentially causing these routers to drop your packets. But, theoretically, one could append tiny amounts of arbitrary data to an ICMP packet. (This is how traceroute works). It's far more common to use an SSL-over-TCP tunnel for proxying: for example, SOCKS, or any of the numerous secure VPN protocols, are much more robust ways to securely tunnel traffic to a trusted proxy server. As far as "tricking" your router: ports are an abstraction supported by the TCP or UDP protocol; you cannot "fool" a router by sending non-TCP or non-UDP packets. Those are simply "invalid" TCP or UDP packets, and as I mentioned, are liable to be dropped, potentially with the consequence of convincing the router to drop future valid data you may wish to transmit. Nimur (talk) 04:57, 2 October 2012 (UTC)

ICMP tunnel AvrillirvA (talk) 10:39, 2 October 2012 (UTC)

low-level ram stuff

i write software as a hobby, and i wanna know if there's any way to keep malware from reading my apps's data from the ram. or if the os may do this for me. more specifically, can my software directly prevent other software from reading the ram it's allocated, or other ram with it's data (like the frame buffer, storing a bitmap of data to be output to the screen)? or can it even detect that other software is doing this? and can the os prevent or detect it? also, can malware open files it doesn't have permissions to (overriding them the permissions)? thanks, 04:24, 2 October 2012 (UTC) — Preceding unsigned comment added by 70.114.254.43 (talk)

If malware is running while your program has things stored in RAM, I can't see any way to stop it from reading it under the current architecture. Still, there are things you can do:

A) Obviously, make sure that no malware is running.

B) Use a computer with no connection to the outside world. This means no Internet, but also no swapping CD's, DVD's, and flash drives with your friends. This would both help to keep malware off your computer, and, if it does get on there, it would also prevent it from sending your data to the bad guys.

C) An architecture with a single process running would prevent this. Embedded systems may do this.

D) An architecture which strictly limits access to RAM by process could be developed. This could work with separate processors, where each processor has it's own RAM, and only runs a single process. The performance hit might not be as bad as you think, as a processor with only a single process could avoid having to "take turns" and swap things in and out of paging space. Of course, you'd need lots of processors and RAM chips to do this for every process (like 256 ?). However, if you only need a few standalone processes, then you could let most of the processes run together on the same processor and RAM, as they do today. StuRat (talk) 04:42, 2 October 2012 (UTC)

We have an article on memory protection that answers most of your question. Provided that the operating system is functioning normally, and that you are not running esoteric computer hardware, it is the job of your operating system to guarantee memory protection. Nimur (talk) 05:06, 2 October 2012 (UTC)

python network programing

what do "socket.setsockopt", and "socket.options", and "socket.ip_ttl" do? and is there any way to change the fields in the ipv4 header? and does the socket module support ipv6? and does python have a way to do arp or rarp? and lastly, does python have a way to build a packet from the ground up (below the transport layer) and send it? thank you in advance, 70.114.254.43 (talk) 04:43, 2 October 2012 (UTC)

Such specific questions about the APIs are best answered by consulting Python's excellent online documentation. For your latter questions: no, Python is a high-level, platform-independent language, and does not have a mechanism to access low-level hardware interfaces such as the direct control of a network interface. Python programs can call external system libraries to execute system-specific functionality. Nimur (talk) 05:12, 2 October 2012 (UTC)

the online docs don't have info on "socket.options" or "socket.ip_ttl". and were would i get software to work below the transport layer (direct control of a network interface)? 70.114.254.43 (talk) 07:33, 2 October 2012 (UTC)

On Linux, socket.setsockopt is a thin wrapper over the setsockopt syscall, and works just like it. As that man page suggests, the options themselves depend on what kind of socket it is. So, for TCP for an example, see the "Socket Options" section of the TCP manpage. Yes, the socket module supports IPv6 - create a AF_INET6 socket. Python doesn't contain built in libraries for ARP and RARP, but you can find several libraries that do ARP at least, or you can build your own in Python (see next question). As to building your own packets - yes, you create a AF_PACKET, SOCK_RAW socket, and you can hand make ethernet frames (see this example); I think you need to be root to open a SOCK_RAW socket. If you make AF_INET, SOCK_DGRAM sockets you can write IP packets (and thus manufacture things like ICMP and IGMP packets), for which I don't think you need to be root. All the above is roughly the same on Windows, but you'd need to look up the MSDN documentation for sockets and their options. Reading and generating packets can be a chore, so packages like scapy make it easier. -- Finlay McWalterჷTalk 11:25, 2 October 2012 (UTC)

On Windows, a raw socket is created with socket.socket(socket.AF_INET, socket.SOCK_RAW) instead. I've checked, and to create a raw socket you definitely need to be root on Linux, or Administrator on Windows. I don't know where you're finding socket.options and socket.ip_ttl I don't see these (either as members of the socket package, or of a created socket), either on Windows or Linux. -- Finlay McWalterჷTalk 12:29, 2 October 2012 (UTC)

Archive a web site

What would be the easiest way to archive an entire existing web site, one to which I only have regular HTTP access to? Horselover Frost (talk · edits) 14:15, 2 October 2012 (UTC)