Wikipedia:Reference desk/Archives/Computing/2011 July 19

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July 19

torrent speed

when i started downloading lost season 3, the speed was like 150 kbps. when it was 25% done, i ended the session. but the next day when i resumed, the speed dropped to 10-20 kbps, or even 5.... and it's still going on... (this is the 3rd day; on my normal speed, the download would have finished by now)

can anyone tell me why? is there something wrong with my torrent or my internet connection? — Preceding unsigned comment added by 117.197.247.76 (talk) 01:21, 19 July 2011 (UTC)

You already asked this question recently; look a little up the page for the answers to it. --Mr.98 (talk) 01:44, 19 July 2011 (UTC)

Cheat sheet program

What program could be used to create documents such as this or this? I can't get Word to do that, and although I could write a GUI in Java, with all sorts of JPanels, there's hopefully a better way. Any thoughts? KyuubiSeal (talk) 05:39, 19 July 2011 (UTC)

Inkscape, or HTML/CSS ¦ Reisio (talk) 06:48, 19 July 2011 (UTC)

Doing this in a word processor isn't difficult. Just create a table and merge-cells as needed, and (for one that resembles the HTML cheatsheet) turn off the borders for cells. The only thing that you might not be able to trivially do is the gradient fills in the Jquery sheet (I don't have a recent version of Word; OpenOffice-Write doesn't do gradients for this). Or you could easily do this with HTML+CSS (gradients too). -- Finlay McWalter ☻ Talk 13:28, 19 July 2011 (UTC)

Oh, darn. I completely forgot about merging cells. The sheet I'm writing is on HTML, so I could do it that way too. Thanks! KyuubiSeal (talk) 14:53, 19 July 2011 (UTC)

Computer attempts to boot, fails, and repeats until unplugged.

Not long ago while plugging in my iPod, I noticed my computer seemed to have electricity running through it (where it's not supposed to run). My hand would feel weird, and start to tingle and then hurt when I touched any metal part on the case, I immediately turned off the computer, unplugged it, took it off the ground, and left it alone for a few days. I came back, opened it up, and made sure my motherboard was properly secured, I determined it was, and that there were no foreign artifacts laying around, closed it up, made sure it was still un-grounded, and attempted to boot it up. It turns on, the fans start spinning, the screen stays black, and then it turns off abruptly. It then, without any user input, attempts to start up again. This repeats until the power cord is unplugged.

I troubleshooted it by taking out parts individually. First the DVD drive, no luck, then the RAM, still no boot, then the Graphics Card, still nothing, finally I removed the heat sink and processor and it finally booted up (as much as it could).

Any ideas as to what could be wrong with it OTHER than the processor? I'm really not looking forward to shelling out a few hundred dollars for a new one.

Regards, EvlD — Preceding unsigned comment added by 76.7.238.176 (talk) 07:18, 19 July 2011 (UTC)

I have no idea what's happening, but my first instinct is that the case is faulty. General Rommel (talk) 08:28, 19 July 2011 (UTC)

It sounds very much like a faulty power supply. These are easily replaced by someone who knows what they are doing, but as General Rommel suggests above, you should first check that the incoming connection is not shorting to the case. Dbfirs 09:25, 19 July 2011 (UTC)

(edit conflict)The "my computer seemed to have electricity running through it" may be the key. If the mains voltage is leaking to the case it could, potentially, be dangerous. ☠ Caution is advised!

If the power supply is faulty that may well explain the "boot up, boot fail, restart loop" the OP is experiencing. (I recall I had a motherboard that had a BIOS setting that caused it to automatically restart after a power failure.)

It was a possibilty that a component had failed causing excessive current drain that might cause the power supply to shut down and re-start. N.b. A PC cannot boot while the RAM is removed!

If possible try another power supply. Or try adding components one by one to see if it causes a failure.

Here are a few links to tech help forums for "computer constant reboot" as the topic: computing.net, techsupportforum.com, certforums.co.uk, and whirlpool.net.au.
As for the final question, the Motherboard itself could be faulty. In the forums it was found that faulty reset switches and evan a HDD LED cable were the problem. - 220.101 talk^\Contribs 09:50, 19 July 2011 (UTC)

Program takes eons to load

I'm trying to use VLC player to stream TV over the local network (that's a whole different set of problems) but it takes upwards of 10 minutes before VLC actually loads/opens from the moment when I click on it. Had a google but no real ideas, thought maybe it was something to do with the new antivirus I just installed, Viper --131.172.80.142 (talk) 09:32, 19 July 2011 (UTC)

...well if you disable the A/V temporarily, you'd know. Alternatively, check how much RAM you have. ¦ Reisio (talk) 18:31, 19 July 2011 (UTC)

PHP

Can I use PHP to create web-based computer algebra systems? 474,456,499 24,485,729 14,939,942 11:37, 19 July 2011 (UTC) (Please answer on my talk page)

Yes. You have one page in which a person enters the data. Then, that page sends the data to the server. On the server, PHP is used to do the calculations. Then, the results are sent back as a new page. If you don't include AJAX, you are limited by using an input-response program. With AJAX, you can use an event-reaction based program. -- kainaw™ 16:10, 19 July 2011 (UTC)

Doing it all entirely in JavaScript is also possible. ¦ Reisio (talk) 18:32, 19 July 2011 (UTC)

Some time ago I created a fairly trivial PHP front-end to the GNU Octave command line. You can download a symbolic algebra system for Octave, and then drive it through a similar web-based PHP interface. All you really need to do is have your PHP program send input and receive output from a command-line.

If you prefer, you can use PHP to drive another computer-algebra system, or try to design your own symbolic representation system yourself, implemented in PHP. Nimur (talk) 21:33, 19 July 2011 (UTC)

PC to TV with HDMI/DVI-D

Hi, I'm wondering if someone can help, I've just got a new LCD tv and I'm trying to hook the PC up to it. I've connected a HDMI to DVI-D (dual link) cable (hdmi at tv side) and a single 3.5mm audio cable between them & there is a picture, but when I try to watch an avi file (using Nero showtime) both the tv & PC pictures go all blocky. When I unplug the cable the blockyness goes away. When I'm not playing a video file the pc picture displays on the tv clearly. Can anyone give me some advice? I'm thinking it must be an issue with the cable (too long? it's 5m, interference?) rather than the graphics card as video plays ok on the pc itself. Thanks AllanHainey (talk) 18:39, 19 July 2011 (UTC)

Blocky artifacts are often a symptom of a computer that is too slow. To be more technical, it means that frame output took place before video decompression was completed. If your graphics card (or computer CPU) can only marginally decode the video when one screen is hooked up, the addition of a second screen (your television) may push the system to its capacity - you may be out of video RAM, or may simply not have enough cycles on your GPU or CPU to produce output for both screens and decode the video at a high frame-rate.

If the issue is visible only with large (high-quality) files, but goes away when you play smaller (low-quality) files, that almost certainly confirms this diagnosis. Consider upgrading to a more powerful graphics card (or CPU) that has better support for dual-display. Nimur (talk) 19:05, 19 July 2011 (UTC)

Thanks, I'll hunt down a small low quality video file to check if there's the same issue & try it with the computer screen unplugged too. Out of interest is there a way to determine whether its a graphics card or CPU issue? - like knowing GPU of X spec can handle up to Y Mb video files?. I'd hate to get a new graphics card & find out it was a too slow CPU. As a related issue where would I check the spec of the graphics card I have installed? AllanHainey (talk) 20:24, 19 July 2011 (UTC)

Video codecs are a little bit "voodoo-esque" - so there's not a straightforward mapping of GPU performance to video-playback-capability. But the thing you want to look at is bitrate, not file size directly. You can also consider installing a better or newer version of your codec: I highly recommend the ffmpeg suite, or ffdshow on Windows. Both are free software and are very high-performance, hardware-accelerated implementations of the standard video and audio codecs in use today. If you use the VLC player, you are already using ffmpeg under the hood. (Installing VLC is a pretty easy fix for many users: download it from the official website). If the video plays "fine" in VLC, but not in other video players, consider switching (or consider instructing your existing video-players to use ffmpeg, by installing the DirectShow filters in FFDSHOW).

The trick is that the performance depends on many many factors. The most important factors are the input (compressed) bitstream bitrate; the output (uncompressed) video size; and the number of encoding features in use (motion vectors, block comparisons, and so on). Each of those parameters were decided by whoever created the video file, and were tuned for file-size, performance, and image quality on the creator's machine. You can use ffmpeg to perform video codestream analysis, but this is a bit more technical than most users want to get. What you really want to determine is (1) whether you can, on average, decode each full frame faster than you need to display it on screen; and (2) what behavior your codec (and video player software) prefer to use if you can't meet that requirement (a dropped frame): the frame can be dropped entirely (all processing on it is stopped, leaving behind the last frame that completed, or a blank screen); or the frame can be rendered before it's ready (resulting in any number of weird-looking images, the least of which include blocky-artifacts).

You can get some ballpark comparative numbers for different hardware configurations from these video and image-processing benchmarks: CPU Core Performance and Graphics Card Performance benchmarks from last month at Tom's Hardware. In some unusual circumstances, your video playback performance may also be limited by main memory (total amount of RAM on your computer); or by hard-disk speed; but those are not commonly the most serious bottleneck on a modern computer. Nimur (talk) 21:12, 19 July 2011 (UTC)

What CPU load does Task Manager report? CS Miller (talk) 11:43, 20 July 2011 (UTC)

Agree if VLC does not "fix" it your computer is too slow, I had same problem using a dual core windows 7 laptop 4GB RAM etc etc pluged into a giant LCD TV; the came-with-it Cyberpathic DVD s/w was a pig but VLC just played those DVD. But nah a dedicated DVD player is almost free and the TV has a USB port for memory sticks, the laptop is now back on my lap! 81.109.247.189 (talk) 22:35, 19 July 2011 (UTC)

Could it be that the TV doesn't support HDCP? If a HDMI source is connected to a DVI-D display, then it is unlikely that HDCP can be established. The program is then informed of this, and can decide not to display the picture, or only display a degraded version of it. CS Miller (talk) 11:43, 20 July 2011 (UTC)

Thanks for the advice guys,

Csmiller - when I'm playing a large video file with both screens plugged in the CPU is showing around 36-42%ish, I'm surprised its as low as that frankly.

I tried running a smaller, less graphics intensive, file and it displays fine, so its not a HDCP thing. I also tried unplugging the computer monitor while playing a large file, but it doesn't make any difference to the picture, still blocky.

VLC works though, I just played some heavy graphics part of a big file & the picture was perfect. So I take it from that that that the performance issues using Nero as a viewer were down to the codecs. I'll look into the ffmpeg, etc codecs & see if I can get them to work with Nero. I could always use VLC but I prefer the layout on Nero.

Thanks for allthe help AllanHainey (talk) 19:56, 21 July 2011 (UTC)

In case I was not clear: if you install ffdshow, many Windows media players will then proceed to use ffmpeg as their preferred codec. The programmer of a video player often designs the video-player-GUI program to "ask" Windows what codec to use; if Nero uses this approach, it will choose ffdshow. If the programmer overrides Windows' suggestion, all bets are off.

In my experience, Windows Media Player, Media Player Classic, WinAMP, and most plugins for Internet Explorer (which are typically just Windows Media Player in disguise) will choose to use FFDSHOW if it is installed. Other video players (such as iTunes, DivX Player, and a few others I have tried) will not use ffdshow, even if installed. I have never tried with Nero. Nimur (talk) 16:25, 23 July 2011 (UTC)

Bytes free on a Commodore 64

The start-up screen of a Commodore 64 says:

    **** COMMODORE 64 BASIC V2 ****

 64K RAM SYSTEM  38911 BASIC BYTES FREE

READY.

The READY. message comes from the BASIC interpreter, everything before that is a start-up message text. However, when I have done a thorough memory search of the Commodore 64 (by using a loop that PEEKs at every single memory location) I have only found the "**** COMMODORE 64 BASIC V2 ****", "64K RAM SYSTEM" and "BASIC BYTES FREE" bits. Therefore the number 38911 has to be dynamically calculated. But on every single Commodore 64 that I have used, it has always been the same. The Commodore 64 doesn't even use the nowadays ubiquitous method of allocating memory dynamically, instead its memory map is fixed. Has there ever been a case where the computer has reported some other number than 38911 as the number of free BASIC bytes on start-up? JIP | Talk 19:03, 19 July 2011 (UTC)

The number doesn't necessarily have to be dynamically calculated, it could be hard-coded as a constant. The source code for BASIC interpreters in those days was written in assembly language, and disassembled versions can be found here and there, so in principle it would be possible to figure out how it worked. Looie496 (talk) 19:26, 19 July 2011 (UTC)

(From my very faulty old memory...) When the system loads, it places the main system at the top of RAM. So, the memory pointer begins at the end of the entire 64k. It decrements as memory is filled with all the background operating stuff. When it is done, it shows where the memory pointer is - which happens to be how much memory is available. If you have faulty memory, you will see something different. That was rare, but I saw it happen to one (and only one) C64. It reported 0 basic bytes free. It was possible to change how many bytes were free by using the cartridge, which could be directly mapped to RAM. An example is Simons' BASIC. (cool - there's and article with a screenshot of the altered basic bytes free!) -- kainaw™ 19:35, 19 July 2011 (UTC)

This may interest you: http://www.pagetable.com/?p=48 2.97.220.86 (talk) 19:49, 19 July 2011 (UTC)

Here are some more details, sure to be either boring or delightful depending on where the C=64 fits on your nostalgia scale:

It's done in 2 layers: first, a probe by the kernal to determine the usable RAM area, and second, the BASIC interpreter deciding to all of it, minus one byte. Note that the 38911 byte BASIC program area is just the largest contiguous chunk of free memory. There is another fairly large unused area of 4096 bytes starting at $C000, between the BASIC ROM and the device I/O ports. That's a good place to store stuff that needs to coexist with a BASIC program, since BASIC won't mess with it.

$FD50 is the early kernal routine that scans memory, starting from $0400 (it scans upward, not downward as Kainaw said). It writes $55 then $AA to each address, reading them back to make sure the write was successful, and stopping when an unwritable address is found. The unwritable address (normally $A000, the first byte of the BASIC ROM) is recorded at $0283, the "top of memory" pointer. There's also a "bottom of memory" pointer at $0281, which gets set to a hardcoded $0800. (The memory from $0400 to $07FF is used as video RAM in the default text mode so it's effectively unusable for other purposes.)

Later, the BASIC setup routine $E3BF queries the kernal for the top and bottom of memory (by calling $FF9C and $FF99) and copies the "bottom of memory" pointer to $2B and the "top of memory" pointer to $37. It increments $2B, making it $0801, and stores a zero byte at $0800. The single zero byte at $0800 is important somehow... if you change it, BASIC gets confused. I don't know exactly why.

After the setup is done, the routine at $E422 prints the startup message. To compute the number before "BASIC BYTES FREE" it subtracts the value at $37 from the value at $2B. In the normal situation, that's $A000 - $0801 = $97FF = 38911. 67.162.90.113 (talk) 21:13, 19 July 2011 (UTC)

A cartridge can contain a ROM which is mapped at $8000-$9FFF, which will overlay (for reads) the RAM normally present there; the write-and-readback on an address confirms that it's not overlaid. There's usable RAM under the BASIC ROM too (and, academically, under KERNAL). The ROM overlays can be switched in or out with pullups on the HIRAM and LORAM lines on the cartridge port. I don't think there's a definitive way to detect (in software) a cartridge (except that, for it to hook the kernal it needs to have a signature at $8004), so kernal needs to check at least the cartridge-rom and basic-rom spaces to see if they're overlaid in the current memory map). But a scan from $0400 is more thorough than that needs (a simple read/invert/write/read at $8000 and again at $A000 would be sufficient). I can't help wonder that, rather than Kainaw's bad-memory theory, it's a holdover from the VIC-20, which could contain a variety of different RAM sizes depending on expansion cards. -- Finlay McWalter ☻ Talk 22:16, 19 July 2011 (UTC)

Indeed, the scan, and the 64's rather bonkers memory map (all that lovely space at $C000 gone to waste) makes a lot of sense if you imagine that, while they were designing the C=64, maybe they were considering selling a cheaper "Commodore 32" (the same machine but with the two high RAM chips missing). Even in a C=32 the CART-ROM, BASIC-ROM, VIC-IO, SID-IO, CIA-IO, CHAR-ROM, and KERNEL-ROM images would all be at the same place; the only change would be that they would need to move the colour-RAM from $D800 (which is a VIC register setting). I stress I've no evidence that a C=32 was ever countenanced, but back in them days when 32k of RAM cost an appreciable sum, having an option for that would make sense. -- Finlay McWalter ☻ Talk 22:36, 19 July 2011 (UTC)

I want to keep bookmarks, but not have them pop up in Google chrome's autocomplete?

Is there any way? I want them organised in neat folders for research but I don't want them interfering with my search results. elle _{vécut heureuse} ^{à jamais} (be free) 22:41, 19 July 2011 (UTC)

In Firefox, you can use bookmarks but disable the "smart completion" in the URL bar by setting the MaxRichResults parameter to -1. I do not think there is an equivalent option in Chrome, by design: Google intends for Chrome to assist you in finding the page you are looking for. Here is some more information specific to Chrome: Predictions in the address bar, and some information for disabling some parts of the prediction service. Nimur (talk) 00:47, 20 July 2011 (UTC)

I'll check that out, but it probably won't solve my problem. Thanks anyway! elle _{vécut heureuse} ^{à jamais} (be free) 07:28, 20 July 2011 (UTC)