Wikipedia:Reference desk/Archives/Computing/2010 April 19

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April 19

Choice of calculator

Go to this website:
http://www.tqa.tas.gov.au/4DCGI/_WWW_doc/009232/RND01/2010_Calculator_Policy_&_List.pdf
Which of these calculators in the list is the most powerful/best? —Preceding unsigned comment added by 203.22.23.9 (talk) 03:09, 19 April 2010 (UTC)

Most powerful for what? Best at what? You need to define the application of a tool before you can ask which tool is best for the job. -- kainaw™ 03:40, 19 April 2010 (UTC)

For example, the TI-89 can perform symbolic computation, including some basic calculus; the TI-83 cannot. Is this a feature you care about? And as I recall, the TI-86, while "weaker" (less RAM, slower CPU) than the '89, had a much more convenient statistical data input tool. So - if you plan to do lots of data input, the '86 may be better; if you plan to do large matrix inversion or 3D plotting, you will need an '89. I seem to recall color graphics on some of the Casios. For a comprehensive comparison of features, consider checking the manufacturers' websites, or see Comparison of HP graphing calculators, Comparison of Texas Instruments graphing calculators, Casio graphic calculators; we don't seem to have articles on Jastek or Sharp graphing calculators (take this as a hint: the user-community for those brands is miniscule by comparison, which may be more relevant than any features they have to offer). Nimur (talk) 03:51, 19 April 2010 (UTC)

On the other hand, even in this modern interconnected and internet world it may still be useful to have something popular where you live among students and teachers alike. What's popular on the internet is not necessarily what's popular locally particularly if you live in a relatively small country (or alternatively developing but not applicable here). Jastek appear to be primarily a NZ and Australian brand, no idea if it's popular in either. Not sure about Sharp but [1] lists some that are touchscreen which it says are unique although I didn't check if they are allowed. However it doesn't seem to be accurate anymore since there's now a Casio ClassPad 300.

P.S. To use an an example of what I'm talking about, the fx-570 and fx-991/992 are the defacto standard calculators in Malaysia (or were but I think it's still the case) used probably by a majority of Malaysian Form 4, 5 & 6 secondary students (most of those who don't would be people who don't use a scientific calculator because they can't afford it and isn't that important for basic maths). And most in university are likely to keep that if they need it unless they can use a graphing calculator. There's another scientific calculator who's model number escapes me that seems quite popular here in NZ although I don't know if the situation here is quite so similar to Malaysia. However the only article we have is apparently on a Casio HS-8. Meanwhile we apparently have articles on 5 TI scientific calculators (although one of them seems historic) but I don't think I ever even seen a TI calculator of any sort in person. Not quite the same thing but does highlight the fact systemic bias may mean what's popular on the internet and wikipedia isn't necessarily popular where you live.

Nil Einne (talk) 06:50, 19 April 2010 (UTC)

I can't think of the last time I even used a calculator, though I have one around here somewhere. They are handy if you have to do simple arithmetic frequently, but "powerful" ones only made sense before the era of cheap computers everywhere. These days for scientific work, use something like Octave, and for business, use a spreadsheet. 66.127.54.238 (talk) 08:52, 19 April 2010 (UTC)

In an exam? Nil Einne (talk) 10:14, 19 April 2010 (UTC)

Yes, in fact many smartphones and some netbooks are actually cheaper than some of these graphing calculators. So, if there were no restrictions, a $150 netbook running GNU Octave or some commercial mathematical software would be a much smarter investment. However, the OP's question specifically indicates that only these calculators are acceptable by the school authorities; other features are not permitted because the school believes those technologies give an unfair advantages, or inhibit learning the material, or some other reason. Nimur (talk) 15:57, 19 April 2010 (UTC)

The reason is that netbooks, smartphones etc. may contain or be able to access unauthorised material or outside help that would give an unfair advantage.

I was wondering if anyone was going to make the point but no one did but I guess the obvious question, somewhat similar to Kainaw and Nimur's earlier points is whether you really need to 'best' (whatever you mean by that) calculator for your purposes, or simply something that's good enough. If calculator A and B will make no difference to you when actually used (which other then exams will also likely be while studying and in classes) and calculator B is cheaper, it'll surely be better to choose B unless you're really rich enough cost doesn't matter. Admitedly I can somewhat understand the urge if you're spending say $100 on a calculator (dunno if that's accurate) and the $130 one is a lot better, to spend that extra $30 even if it's somewhat unlikely you'll ever actually gain much advantage or use those extra features. Nil Einne (talk) 09:16, 20 April 2010 (UTC)

advanced format

I'm thinking of getting a 750gb WD hard drive for my laptop (my current 320gb is full). This is the largest (and only) laptop-sized drive of such high capacity, but I notice it uses Advanced Format. Should I care? I'm running a fairly recent Linux distro, and the main contents of the 750gb drive will be relatively static files, (I also have a flash drive in the machine). The disk will be encrypted with dmcrypt/LUKS. I'm wondering if advanced format will introduce awful slowdowns if the dmcrypt layer does 512 byte i/o and the advanced format ends up splitting a bunch of consecutive 512 byte operations into separate access to the same 4k sector, each needing a full disk rotation. I can alternatively get a 640gb drive at some cost savings per GB, but I figure 4k sectors will be upon us eventually no matter what. 66.127.54.238 (talk) 08:59, 19 April 2010 (UTC)

The kernel should support it - I've not found which version added support, but the 2.6.31 (which is what Karmic runs, and apparently what Gentoo features) apparently does. But it seems the tools are a bit slower to catch up, and you may need to manually arrange partitions to avoid performance problems. I think all the tools (fdisk seems to be the chief one of note) are caught up now, but I'm not sure that distributions (which often lag upstream by a fair amount) will have the correct versions. Here are some relevant articles: OSNews h-online -- Finlay McWalter • Talk 09:28, 19 April 2010 (UTC)

I should clarify that my post above is just to get decent performance on regular, unencrypted use. I don't know how dmcrypt will handle the bigger sectors - it appears to assume sectors are 512 bytes at the command line. I've found a patch from 2006 that someone proposed handling for bigger sectors, but I don't know if they included that in the mainline. It is possible to determine the sector size of a device with the BLKSSZGET ioctl, so there's no reason for them to not support this. -- Finlay McWalter • Talk 10:28, 19 April 2010 (UTC)

Thanks, those articles make me think I should wait a while before buying an AF drive. I will stick with a smaller drive for now, and see about migrating some of my less-used data to an external drive. 66.127.54.238 (talk) 18:03, 19 April 2010 (UTC)

There are no compatibility problems with any OS or software. The drives still claim to have 512 byte sectors (and will forever, I imagine; there's no benefit to breaking backward compatibility). They have a large internal cache (like all hard drives from the past decade or two). Each 4K physical sector is read once and reads of the 512-byte logical sectors come from the cache. 512-byte writes are coalesced before going to the disk. The only problem is that you might see reduced performance on random writes if your filesystem clusters are misaligned with the physical sectors. You can avoid this problem by partitioning and formatting the drive correctly when you first get it. If, for whatever reason, you don't partition the disk correctly in the first place, you can subsequently run WD Align, which realigns the existing partitions on the disk. If the drive is partitioned and formatted correctly, you will have no further problems with any OS. -- BenRG (talk) 10:03, 20 April 2010 (UTC)

How to improve this ERD for a Mysql database

I have been asked to develop a PHP script for this form http://www.scorpionagency.com/imagehosting/uploads/782694a43c.jpg . User can register by choosing and username, password ,email and this form will be used to enter his/her information. For the moment, I have only designed the important tables, as other tables such as the one holding country names would be easy and i have not included them in the design. Could you please say how i can improve this design http://www.scorpionagency.com/imagehosting/uploads/33c939092a.gif ? —Preceding unsigned comment added by 89.244.144.251 (talk) 10:51, 19 April 2010 (UTC)

In general, you seem to have designed the table to match the form exactly. I'd caution against this. Let's say they decide they want to add another activity. Should this require redesigning the database ? No, it should be flexible enough to allow for such changes. Some more specific thoughts:

1) It would help if you could define the variables. For example, what are "company businesscodes" ? Does this identify which industry they are in ? What are "company destinations" ? What is "distribution" ?

2) You use a single "telephone" field which is VARCHAR(40). They may have more than one phone, such as a cellular/mobile phone. Thus, you need to allow for multiples and a way to identify when to use each (like "when at home" or 6 PM - 9 AM). Also, be aware that a single character field allows for lots of flexibility (like extension numbers), but sometimes that's too much flexibility. For example, you could end up with phone numbers in all of these formats: "123-456-7890", "123.456.7890", "(123)-456-7890", "1234567890". You'd need to standardize the method of phone number entry to prevent this.

3) Same comment for only allowing a single e-mail address. Also, why is the e-mail address in two different tables, and with two different lengths ?

4) Whenever you start numbering columns of a table, that's a clue that you may need an additional table or a different table structure. Perhaps not for "address1" and "address2" (which I guess are lines 1 and 2 of the street address), where you can assume that the address is only 2 lines long (or can at least be crammed into 2 lines, excluding the company name and city/province/postal code line). However, "company activities" seems to assume that no company will ever have more than 4 activities, which is a bad assumption. StuRat (talk) 15:54, 19 April 2010 (UTC)

Thank you. As you can see, I have very little idea about creating a normalized database. If you can tell me how to make it flexible, I would be glad to do so, even if it involves complete re-design. "company businesscodes" refers to the area of businesses they are in. "company destinations" refers to tourist destinations they are dealing with."distribution" refers to channel of distribution like cd rom, internet etc. could you please suggest a better idea for 2 address lines?. —Preceding unsigned comment added by 89.244.144.251 (talk) 08:10, 20 April 2010 (UTC)

1) The variable names should be clear to everybody without having to look them up in a key. Some suggestions:

businesscode        = industry
company destination = national destination
distribution        = info delivery method
address1            = address line 1
address2            = address line 2

2) Before I can suggest a solution for phone numbers, I need to know what you want to allow. Can they enter multiple phone numbers ? Can phone numbers be of different types (land-line, mobile, etc.)  ? What format should be used to store phone numbers ? Are extensions allowed ?

3) Similar questions for e-mail address.

4a) I thought the 2 line address was OK. You could maybe extend it to 3 or 4, if you want, but there's a definite small number of lines in any address. I didn't like "address1" as a name, though, since that implied, to me, that it was the first of two addresses, when you actually mean the first line of a single address.

4b) "Activities" are different. There could be any number of those, right ? In this case, reduce the 4 columns to just one "activity" column and allow a new row for each activity. The "distribution" field doesn't really belong in this table, though, as it doesn't vary by activity. StuRat (talk) 14:45, 20 April 2010 (UTC)

What makes a CD bootable?

I have a number of computers at home and have never had a problem producing a bootable CD, but I have found that not all my "bootable" CDs can actually be booted from in some cases. I recently acquired an old used Sony laptop, but it came with no installation CDs. In an attempt to fix problems with the Windows XP Professional installation, I booted (successfully) from another computer's OEM XP Professional installation disk, carried out a repair installation and then ran into Windows activation problems (as detailed in this previous question). It seems these problems are insurmountable unless I am prepared to buy new XP installation disks; which I am not. I thought instead I might try out various Linux Live CDs to find one I liked and had acceptable performance on the Sony laptop; and this is where the problem began. Even though I can boot off my XP installation disk and one Linux Live CD, there are two others which refuse to boot with the CD just sitting in the drive clicking but not actually doing anything. When the CD is removed, the PC boots normally into the repaired XP installation that can't be activated. It is probably worth pointing out that all the CDs are actually bootable and work as expected in other computers. So, is there something that makes a CD bootable, something the BIOS is looking for which might be missing from these two CDs. The boot disk article was not particularly helpful. Astronaut (talk) 14:33, 19 April 2010 (UTC)

The El Torito (CD-ROM standard) article should tell you what you need to know. As far as I can see, a machine either does or doesn't support El Torito bootability. It could be that there's some other extension to the ISO9660 CD-ROM specification that your machine doesn't support, that's used by the problematic disks. --HughCharlesParker (talk - contribs) 15:05, 19 April 2010 (UTC)

It may not be the format per se that's different, but the disk (either physically or its low-level format). Some older drives are unduly picky about stupid things, so here are some things to try:

• you're definitely using CD-R and not DVD-R media, right? You can burn a CD .iso onto a DVD and most computers will be perfectly happy; but a few might not.
• you're using CD-R media and not CD-RW (some older drives don't like RW media).
• the disk is single-session and finalised for burning an .iso (you'd expect this, but you never know).
• try substituting a different manufacturer of CD-R, incase the drive just doesn't like disks of one brand.

That's all straw-clutching, but worth a go. -- Finlay McWalter • Talk 16:47, 19 April 2010 (UTC)

bug fixing

what is bug fixing? is it a BPO job? —Preceding unsigned comment added by 220.227.88.34 (talk) 15:22, 19 April 2010 (UTC)

It is about fixing software bugs. It is unlikely to be undertaken as part of business process outsourcing, unless the creation of the software was itself outsourced. In short, bug fixes are normally undertaken by whichever company was responsible for creating the code, since they have the most familiarity with the process. --Tagishsimon (talk) 15:32, 19 April 2010 (UTC)

I was once brought in as a contractor to fix bugs in software written by others. What fun ! StuRat (talk) 15:38, 19 April 2010 (UTC)

Mediawiki - automatic content for a new page

Hi. I'm setting up a mediawiki installation, and I'm looking for a mechanism whereby a new page in a particular namespace has default content, as happens when a new page is created on wikia:lyrics. I can't work out how this is done - can anyone help me? --HughCharlesParker (talk - contribs) 15:28, 19 April 2010 (UTC)

Never mind, I found the answer from this forum post - thanks Gregra. The answer is to use mw:Extension:PreloadManager. --HughCharlesParker (talk - contribs) 19:15, 19 April 2010 (UTC)

...except that it doesn't work. Curses! I've posted a question on a forum, asking if anyone knows the mediawiki codebase well enough to work out what's wrong with it, and if anyone can help I'd be very grateful. --HughCharlesParker (talk - contribs) 09:45, 20 April 2010 (UTC)

...and now I've found an alternative that does. I found mw:Manual:Creating pages with preloaded text, which pointed me to mw:Extension:Preloader. I tried it, and it works. Hooray! I hope this little conversation I've had with myself is useful to someone :) --HughCharlesParker (talk - contribs) 21:34, 20 April 2010 (UTC)

NES/SNES

Why was the name changed? Does it mention anything about this in the article? Chevymontecarlo. 17:41, 19 April 2010 (UTC)

NES is a different device from a SNES, a later and more advanced product. The NES was known as the Famicom in some markets; see regional differences in our article for details. Nimur (talk) 17:44, 19 April 2010 (UTC)

Nintendo Entertainment System was the first one; Super Nintendo Entertainment System was the second one. Comet Tuttle (talk) 20:18, 19 April 2010 (UTC)

The two are not one and the same; the Famikom/NES (80's) is the predecessor to the Super Famikom/SNES (1990). —Jeremy ^{(v^_^v Dittobori)} 21:15, 19 April 2010 (UTC)

Perhaps the questioner is wondering why the devices were not called "Famicom" and "Super Famicom" outside of Japan? APL (talk) 21:25, 19 April 2010 (UTC)

I was just wondering why they had such similar names - it's been answered now but it would be interesting to know why they weren't called that outside Japan. Is that in an article somewhere? Chevymontecarlo. 11:48, 20 April 2010 (UTC)

delete irc channel?

is there a way to delete an irc channel? i created one and im the operator in it but i dont want it anymore.--Monky9q (talk) 19:11, 19 April 2010 (UTC)

The server will cease to serve the channel if there are no members in it. Unless the server operates a channel registration service or bot, there is no way to prevent somebody else from re-creating the channel. Nimur (talk) 19:15, 19 April 2010 (UTC)

For your perusal, here is the RFC specifying the technical implementation of a channel: RFC1459. "In IRC the channel has a role equivalent to that of the multicast group; their existence is dynamic (coming and going as people join and leave channels) and the actual conversation carried out on a channel is only sent to servers which are supporting users on a given channel." Individual IRC daemons (implementations of the protocol) may choose other methods to extend channel management, but technically a "channel" is just a short-name the relay servers use to refer to all members of a multi-cast group. Channels never "exist" unless there are members. Nimur (talk) 19:18, 19 April 2010 (UTC)

ok how do i see what channels i have operator status on? i did it somehow earlier and saw i had operator on three chans.--Monky9q (talk) 19:20, 19 April 2010 (UTC) nvm i got it figured out thanx guys.--Monky9q (talk) 19:24, 19 April 2010 (UTC)

Malicious popups

I keep my machine up to date (windows xp, firefox 3.6) all plugins disabled except for flash, java, and mozilla's built in plugins, but even using the most up to date firefox, and with popups blocked (no external extension, just the built in one), some (almost always shady) websites manage to have popups that steal focus, sometimes with prompting boxes that only allow "ok" as the answer. What are the various mechanisms that permit unexempted popups like this? I assume it's either javascript or flash, but at least for javascript, all of my settings disallow that behavior, and traditional popups should be (and for respecting websites are) blocked. So how do the others get through? Shadowjams (talk) 23:04, 19 April 2010 (UTC)

<a href="http://www.google.com" onclick="window.open(this.href, '_blank', 'width=800, height=600, status=0, toolbar=no'); return false;">Link</a>

Why does it work? Because no one would want to block pop-up windows that they asked for. You click on a link to a pop-up music player, and of course a pop-up opens. Pop-up blockers block unsolicited pop-ups, and as soon as you click on the link to the pop-up, it is no longer unsolicited. The onclick event handler can be added anywhere on the page, so as soon as you click anywhere on the page, it is triggered.--Best Dog Ever (talk) 23:47, 19 April 2010 (UTC)

In my experience it's Javascript that's the problem. Disabling that solves the problem, but also makes lots of good stuff no longer work, too. StuRat (talk) 04:14, 20 April 2010 (UTC)

Ok, that makes sense. So it's always the onclick handler in all of those instances? I always assumed that it was the target page. For instance, I clicked on a link out of a reliable news-reader, and got the popup. I know the reliable news-reader wouldn't have referred me to the ad-link, but perhaps there are redirects and then the onclick is inherited through them?

Now that I think about it, it seems like the page actually did open in a tab, it just had a very obnoxious java-script box that came up, and wouldn't go away. So this is slightly a different question, but why do the persistent javascript (I assume it's javascript) prompting boxes (a box with OK [download this spyware] or CANCEL) come up, even if I had those supposedly disabled as well? Shadowjams (talk) 06:04, 20 April 2010 (UTC)

If you're using Firefox, then only JavaScript can do those things. (VBScript only works in Internet Explorer.) Flash can only create popups by calling JavaScript functions. It's important also to distinguish between pop-ups, confirmation dialogs, and alert boxes. Confirmation dialogs and alert boxes are not blocked by pop-up blockers because they aren't technically pop-ups. They lack graphics, but often appear when you try to exit a page. In that case, they are triggered by the onunload event handler:

<html>
   <body onunload="alert('Bye. I hope you enjoyed your stay.');">
   </body>
</html>

--Best Dog Ever (talk) 01:35, 21 April 2010 (UTC)