Wikipedia:Reference desk/Archives/Computing/2015 November 4

= November 4 =

Chrome problems?
Are there problems existing now with Chrome that would make it unable to access some ordinary web sites? I have six sites up right now, and one tab is stalled. I can access this site from Firefox and IE. Halcatalyst (talk) 03:16, 4 November 2015 (UTC)


 * Here is a current list of bugs/issues, here's how to report a problem , here's a little more about bug tracking and reporting for the project . SemanticMantis (talk) 05:24, 4 November 2015 (UTC)

Simplification of CFG
Can we simplify the grammer given below(Grammar 1) into the one below(Grammar) that.The first grammar is in the Article on Synatax Analysis(P.129).

Grammar 1

R → S | R “|” S

S → T | ST

T → U | T*

U→a|b|...

U → “ε”

U → (R)

Grammar 2

R → S | R "|" S | SR

S → S* | "ε" | (R) | R |a|b|.... JUSTIN JOHNS (talk) 09:46, 4 November 2015 (UTC)


 * I think they generate the same language, but Grammar 1 is unambiguous and Grammar 2 isn't, so it may not be a useful simplification in context. Note that since Grammar 2 has R → S and S → R productions, you can simplify it further by merging R and S, and that gets you (back to) the grammar of page 120. -- BenRG (talk) 17:19, 4 November 2015 (UTC)

Could you explain how can we merge R and S from Grammar 2 to get back the grammar of page 120.JUSTIN JOHNS (talk) 06:25, 6 November 2015 (UTC)

Is Hidden Left Factors an issue in Parsing?
It's true that left factoring solves the issue when common prefixes on the right side of the production.I would like to whether hidden left factors creates an issue in parsing as given in Formal Grammars(P.9) since at the first parse the parser might be confused to apply which production when common prefixes appear on the right side of production.While if there is hidden left factors does it create any issue in first parse when common prefixes doesn't appear on the right side of productions?JUSTIN JOHNS (talk) 10:04, 4 November 2015 (UTC)


 * It creates problems for parsers because the sentence to be parsed doesn't contain any nonterminals. If you have B → abB | daA | Af (the example from that handout) and the sentence to be parsed as a B starts with da, the parser can't choose between B → daA and B → Af unless it knows that A can't produce any sentences starting with da. Looking for A in the sentence won't help because A doesn't appear in sentences. -- BenRG (talk) 17:38, 4 November 2015 (UTC)

Could you make clear what you meant by "unless it knows that A can't produce any sentences starting with da".JUSTIN JOHNS (talk) 06:30, 6 November 2015 (UTC)

SATA M.2 vs PCIe M.2
If I buy a laptop with a SATA M.2 SSD, can it be upgraded to a PCIe M.2 SSD later? Or will I be restricted to SATA M.2 SSDs? Thanks --RM — Preceding unsigned comment added by 203.199.213.3 (talk) 18:27, 4 November 2015 (UTC)


 * It looks like it, though you specifically need an M.2 SSD. You can't buy just any PCIe SSD, as the majority are for desktops and use the larger desktop motherboard PCIe slots. --71.119.131.184 (talk) 21:11, 4 November 2015 (UTC)

Resonance and Reactive Power with Square Wave AC
If a capacitor or an Inductor is powered with a square wave ac supply will they be able to exhibit properties such as resonance and draw reactive power like they will do with a sine wave supply?--Adenola87 (talk) 22:33, 4 November 2015 (UTC)
 * Yes. Passive devices like capacitors and inductors behave mostly linearly - so this means you can use linear superposition to analyze the square wave as the sum of many separate sine waves with separate frequencies and amplitudes.  For practical purposes, the power from each frequency does not interact with the power from any other frequency (because the components are well-modeled as "well-behaved" linear systems).  Nimur (talk) 22:42, 4 November 2015 (UTC)

MozyHome backup/restore
I've used the MozyHome backup/restore system for some time. Recently I restored, but some files wee missing. After several rounds on chat support, I am told that Mozy does not necessarily back up files/folders that were added after the initial backup took place. How can this be? Is this standard practice for this type of service? The agents I talked to all seemed to presume that I had (or should have) configured all sorts of settings, and I don't even remember ever having had the opportunity to do so. Halcatalyst (talk) 22:45, 4 November 2015 (UTC)


 * Our article does appear to confirm that after the first backup Mozy by default only takes incremental backups of files that existed at the time of the first backup. That does seem to me to be unexpected behavior that's likely to bite users. I can't give you any specific data on how common this behavior is. Personally I'm a bit of control freak anyway, and stories like this just make me even more determined to avoid commercial "backup solutions". rsync for the win! --71.119.131.184 (talk) 01:30, 6 November 2015 (UTC)
 * The files it skipped for me seem to be random, so I just don't get it.
 * rsync sounds good, but I'm far too non-technical for that!
 * What about backing up into a cloud? What are the pros/cons of that? Halcatalyst (talk) 02:08, 6 November 2015 (UTC)


 * The saying I am fond of is that "cloud" is just another word for "someone else's computer". In general having remote backups is a good thing. Ideally you want both local and remote backups. But you have to take into account the reliability of the hosting party. If they disappear one day, there go the backups you've stored there. And if your data is not encrypted securely, the other party has access to it, as does anyone who might gain unauthorized access. Again, none of this makes remote backups a bad thing. They're just factors to take into account. --71.119.131.184 (talk) 06:26, 7 November 2015 (UTC)

Here's the full story. When you sign up with Mozy, you specify the types of files you want backed up: document, pictures, videos, etc. The filetypes (what does "filetype" mean to the average user?) underlying these categories, and no other, will then be backed up, unless you take positive action to add others. I certainly didn't understand that when I started with them in 2010, and it only became clear the other day when an agent explained it to me.

However, there is a happy ending: the Mozy manager telephoned me and we had a long talk. In the end, he offered me generous support going forward, including direct access to his technicians. And Best Buy was able to complete a file transfer from my dead computer's hard disk. It took 11 hours, because of power problems with the HD. But I have all my files back!

Thank you all for your help. Halcatalyst (talk) 23:28, 7 November 2015 (UTC)

Mother board reliability
How reliable are todays desktop motherboards? When they fail, what is it that most often fails?109.144.180.19 (talk) 23:34, 4 November 2015 (UTC)
 * For me, motherboard failure is very rare, except  Capacitor plague got me once. GangofOne (talk)
 * I've also found them to be robust. I've had network ports blown during lightning strikes back in the ADSL days, but nothing more serious. I've found case switches to be prone to power surges, and most often it's the PSU or power supply which dies after a power surge. Sandman1142 (talk) 12:21, 5 November 2015 (UTC)


 * It is very rare that I've seen a motherboard failure that wasn't user error or a bad power supply, which I don't consider part of the motherboard. 209.149.114.132 (talk) 13:13, 5 November 2015 (UTC)


 * As GangofOne sort of hinted at, on the past capacitor plague was resonably common cause of failure for motherboards. This is a lot less commom now, still I wouldn't say it never happens and (discounting user error) is probably the most common cause of failure (that or the VRMs). I've also had intermited problems which are probably because of the board (without apparent capacitor plague I mean), such as cold boot issues. Nil Einne (talk) 13:52, 5 November 2015 (UTC)
 * Well first off, I had aproblem with not being able to get a new printer to work via usb. Sometimes the compurter would recognise the printer and sometimes it wouldnt. At no time could I get the printer to print from the comuter. Some fiddling with the usb connectios would sometimes change the computers ability to recognise the pri ter. Then I looked at the usb main ports and found them filled with dust as they are near to the main fan which was also clogged with dust. I cleaned both fan and ports and retried printer again without sucess. Now howevdr the computer refused to recognise the printer at all . ? After the umpteenth reboot the computer refused to start and I got the bsod telling me to remove new hardware and drivers etc. Removed alll new hardware. Still wont bbot.31.55.64.30 (talk) 23:12, 6 November 2015 (UTC)


 * Thee are motherboard manufacturers `who do the kind of things things that we electronics engineers normally do when we are designing for high reliability.


 * For example, the Gigabyte ultra-durable line ( http://www.gigabyte.com/microsite/98/html/technology-guide-ultra-durable-f.htm ) has a lot of the design features that I use when designing something that will go on a commercial aircraft. --Guy Macon (talk) 17:38, 5 November 2015 (UTC)
 * Yeah but is it possible that a transient or semipermanent motherboard fault could trash files on the hard disk?86.187.188.120 (talk) 00:31, 6 November 2015 (UTC)
 * It's certainly possible, since the motherboard is how the computer components talk to each other. But, the most common hardware-related cause of data loss is hard drive failure. Is there a specific issue you're having? If so, can you give us the exact details? --71.119.131.184 (talk) 01:35, 6 November 2015 (UTC)