Wikipedia:Reference desk/Archives/Computing/2013 March 3

= March 3 =

Does a computer need separate RAM if it uses a SSD?
From what I understand, SSD is basically non-volatile RAM right? So why does a computer still need volatile RAM in addition to an SSD? ScienceApe (talk) 00:28, 3 March 2013 (UTC)


 * Because SSD is much slower than RAM. StuRat (talk) 00:29, 3 March 2013 (UTC)


 * So then is it possibly to build a computer using an SSD but not have any extra RAM? ScienceApe (talk) 03:27, 4 March 2013 (UTC)


 * Possible, yes, but it would be very slow. Why would anyone want that ? StuRat (talk) 04:02, 4 March 2013 (UTC)


 * First of all, SSD is not "non-volatile RAM". The transistors that make up SSDs and RAM are nowhere near the same. The maximum transfer rate of DDR3-1600 is about 12.8 GB/s, which is about 20 times faster than the maximum transfer rate of a SATA3 SSD. Furthermore, this value is only for sustained transfer rates. You also have to take into account the latency, or basically how fast after you tell it to read something before you get the data back. For RAM, this is measured in nanoseconds, and SSDs are measured in microseconds. This is basically a difference of 3 orders of magnitude. Short answer, SSDs cannot come close to replacing RAM at this moment in time. --Wirbelwind( ヴィルヴェルヴィント ) 02:59, 3 March 2013 (UTC)


 * If it's not "non-volatile RAM" then why does it say in Non-volatile random-access memory that flash memory and other memory used in SSDs ARE non-volatile RAM? ScienceApe (talk) 03:22, 4 March 2013 (UTC)


 * They're non-volatile in the sense that they don't lose information when the power's turned off. They're not the same as RAM. I think that's the point made above. Shadowjams (talk) 07:15, 4 March 2013 (UTC)


 * In the strict sense flash memory etc. is random access memory in that that data can be accessed in any order, hence "random access". Most people actually use RAM colloquially to mean something that is/can be used as primary storage (specifically the "main memory" component of the primary storage - see the diagram in the linked section), whereas at the moment NVRAM such as flash is only really suitable as secondary storage due to the speed issues mentioned above. Equisetum (talk &#124; contributions) 12:58, 4 March 2013 (UTC)

64GB SDHC Cards
I am seeing a lot of advertisements in the web (mostly ebay) for 64GB SDHC flash memory cards. Our Secure Digital article states that the maximum capacity for SDHC is 32GB, and that SDXC supports capacities above that. This is supported by the SD Association web site. Also, I have looked at many brand name web sites and they all consistently apply the SDXC logo to their 64GB and larger cards. This leads me to conclude that the most or all of the 64GB "SDHC" cards on the market are likely fakes (low capacity cards altered to fake a higher capacity).

However, a couple of the sellers that I have contacted say that they have tested their drives using h2testw.exe and confirmed a full 64GB capacity (less a couple of GB of overhead). Assuming good faith, that leads me to speculate that perhaps that these these cards are unsanctioned extensions to the SDHC format. The FAT32 file system can certainly support capacities beyond 32GB, so it seems feasible, although probably not a valid use of the SDHC licensed logo. To be usable though, target devices would need to support these oversized cards, which leads to my question.

Is anyone here aware of any devices (phones, MP3 players, cameras, etc.) that document support for 64GB SDHC? -- Tom N (tcncv) talk/contrib 03:22, 3 March 2013 (UTC)


 * Are you sure they're really SDHC cards? I don't think SDHC can support more than 32 GB, period. If you get a 64 GB "SDHC" card and use it in an older device (even a Droid X), it will not work. I think it's just mislabeling, since most people have not heard of SDXC. Most users probably don't even know SDHC. --Wirbelwind( ヴィルヴェルヴィント ) 05:09, 3 March 2013 (UTC)


 * As far as I can tell from the Physical Layer Simplified Specification Ver3.01, there is no difference between SDHC and SDXC except that cards larger than 32GB are called "SDXC". This is supported by version 2.00 of the spec (found via Google) which says nothing about SDXC but has the same size field with a maximum of 2 TB. Despite this, the version 2 spec arbitrarily limits the card size to 32 GB for no readily apparent reason. My best guess is that it's because recent versions of Windows refuse to format volumes larger than 32 GB as FAT32, and they anticipated needing exFAT, associated compatibility problems, and the need for a rebranding. However there's nothing preventing you from formatting a larger card with FAT32 using third-party tools (or a smaller one with exFAT). The 64GB SDHC cards could be 64 GB cards formatted with FAT32, or maybe the sellers just want their listings to come up when people search for "SDHC". I can't help you as far as device compatibility goes. There's no reason that I can see for a SDHC reader not to support sizes up to 2 TB, but the standard doesn't require them to, so I'm sure many of them don't. -- BenRG (talk) 05:34, 3 March 2013 (UTC)


 * Thank you very much for the specification link. Scanning the document, I can see that both SDHC and SDXC use a 32 bit address to identify the 512 byte block being references, yielding the 2TB (512 * 2^32) limit.  In fact, a search for SDHC shows that nearly every reference is of the form "SDHC or SDXC".  I'll study it further.  As for Wirbelwind comment regarding mislabeling, the cards in question are actually stamped with the "HC" logo along with the 64GB capacity, so it is not just a listing title issue.


 * I would be interested in hearing from anyone who has actually used one of these 64GB SDHC (not SDXC) cards in a device and utilized the memory in excess of the 32GB boundary. --  Tom N (tcncv) talk/contrib 06:23, 3 March 2013 (UTC)
 * This wasn't exactly what you asked about, but some devices which only support SDHC have no problem with FAT32 formatted SDXC cards (i.e. 64GB or higher) even though they may advertise their limit as up to 32GB. (I actually don't know how often it is that you have to format it as many devices will allow you to format the card. It is obviously possible some devices although able to format cards, will refuse to properly format a 64GB+ card but will work with all the capacity if it's already formatted.) E.g. this is quite common with Android devices and I think I've heard it with some digital cameras as well. As BenRG says, there's no particularly reason why a device would not support such a card, but since it isn't part of the standard (even if the potential is there), there's no reason why they have to support it either. I wouldn't trust any card labelled as SDHC greater then 32GB since as you say there are a large number of fakes. (But actually I'd rarely trust any card on eBay.) However it wouldn't surprise me that some cards with a genuine capacity greater then 32GB are labelled SDHC simply because there's no reason why someone couldn't get a manufacturer with genuine 64GB cards to label them SDXC. Heck I could probably get someone to do it myself if I had any desire to buy a few hundred or thousand or whatever the MOQ for labeling is. Of course, even if a card genuinely has a capacity greater then 32GB it may still be a POS. In other words, there's no good reason why anyone in the know would want to buy one of these SDHC labelled 64 GB or greater cards (just buy an SDXC and reformat it if needed, in fact it wouldn't surprise be if some of these SDHC 64GB+ cards are formatted with ExFAT), but also no reason to think that they don't exist amongst the fake capacity ones. Nil Einne (talk) 12:40, 3 March 2013 (UTC)

"Apple Works"
In the good old days before Lion, Apple Works was an excellent programme. It contained a word processor, database, drawing, painting and presentation programmes. is anyone aware of a cheap, (free?) application that I can us with similar facilities please? I particularly regret not having the 'drawing' programme that could be used within the word processor.85.211.211.98 (talk) 16:23, 3 March 2013 (UTC)


 * LibreOffice. -- Finlay McWalterჷTalk 16:27, 3 March 2013 (UTC)

Looks good! Thanks.85.211.211.98 (talk) 17:12, 3 March 2013 (UTC)

Archive
Does the append function in GNU Tar read through the existing tar file first before appending? On a tape drive, would this not take a very long time assuming the tar archive was large? 92.233.64.26 (talk) 19:06, 3 March 2013 (UTC)


 * Yes, that's my understanding too. A conventional TAR or USTAR format doesn't have a manifest/index (unlike ZIP) so you can't know at the beginning where the end is. When I still did tape backups (it's been a few years) I'd use mt at the end of a tar run, and record somewhere the position in the tape that tar had ended at. If I needed to add more stuff to that tape, I'd again use mt to seek to that position and do a fresh tar operation (not an append), creating a distinct new tar archive. Seeking on the tape is, naturally, usually an order of magnitude faster than reading. -- Finlay McWalterჷTalk 23:27, 3 March 2013 (UTC)


 * The few times I've used tape backup schemes that had been set up by older, wiser people than I (people for whom tape had been the only possible backup medium) it seems they'd all cooked up a scheme where the start (or the end, in one case) of the tape contained a special "directory" thing they'd constructed, which had the tape's ID and a basic index showing the dates, sizes, and locations on the tape into which they'd done a tar run. Essentially they'd build rather naff file systems with Korn shell scripts. -- Finlay McWalterჷTalk 23:35, 3 March 2013 (UTC)

Household security
What is on the market now for low-cost video surveillance? An editor in another thread has brought up concerns about a relative's house being an issue because of its notability. I do remember software that was wired to security cameras that would activate with motion. The screen would have a grid layout for each camera and the sensitivity adjusted in each grid square to avoid nuisance activation. If motion was detected at a high enough threshold it would record to hard drive, send emails, activate phone dialers, etc.--Canoe1967 (talk) 19:08, 3 March 2013 (UTC)


 * If the idea is to be able to use the video to identify the prowlers, in low light, when they aren't looking directly at the cameras, that's quite a difficult task, unless they do you a favor by wearing a distinctive jacket, etc. A lower cost solution is just motion detectors which set off alarms and/or lights.  Of course, this just scares off prowlers, it doesn't catch them.  Aiming the motion detectors so they don't cover the ground will avoid them being triggered by cats, dogs, etc.  Also, if it just turns on flood lights, that might scare off prowlers without waking the residents, if that's your goal.  In this case, false alarms aren't so bad. StuRat (talk) 19:16, 3 March 2013 (UTC)
 * Can something like an Arduino be used as an IO to turn on lights from camera software or start recording camera video to hard drives if a light sensor is activated?--Canoe1967 (talk) 23:00, 3 March 2013 (UTC)


 * Seriously, just search amazon for cameras. It depends on your budget. There are plenty of sub $100 cameras, but they do badly in low light. Cameras that do well in low light are going to cost you more. The web-enabled cams are good too, and have been around for almost a decade. There's lots of options. Just search google for them. Shadowjams (talk) 07:12, 4 March 2013 (UTC)


 * A search for 'video security systems' gave many results for systems, reviews etc. I can see prices from a few hundred dollars depending on the scale of the installation.  It shouldn't be hard to find something to suit your installation and budget.  Astronaut (talk) 17:43, 5 March 2013 (UTC)

Connection
I have an laptop running Trisquel and a desktop computer running Windows, but only the desktop is normally connected to the Internet. Giving the laptop Internet access should be as simple as taking the Ethernet cable from one computer to the other, but that doesn't work. The network status on the laptop appears to be loading for several seconds, then I get a notification saying "Disconnected, you are now offline" and then the process starts all over again. — Preceding unsigned comment added by 96.55.96.121 (talk) 19:08, 3 March 2013 (UTC)


 * I am not experienced in the topic, but it sounds like what you want to do is set up Internet Connection Sharing. That article has a few links at the bottom to Microsoft articles on how to set up such a connection.  --  Tom N (tcncv) talk/contrib 21:38, 3 March 2013 (UTC)
 * I followed the steps on the article about Windows 7 but when I go to the network's properties there's no Sharing tab. — Preceding unsigned comment added by 96.55.96.121 (talk) 22:29, 3 March 2013 (UTC)
 * I usually phone my ISP on issues with this stuff. Is it possible that your router needs a cfg for the laptop or the laptop needs a cfg for the router?--Canoe1967 (talk) 23:06, 3 March 2013 (UTC)
 * Trisquel is just a normal Linux distribution. You could use Windows Internet Connection Sharing via the Windows desktop, but that seems an excessively complex setup and is largely superceeded by much simpler methods that don't rely on the Windows machine being on all the time.  Assuming the laptop has an ethernet port, why not simply connect the laptop directly to your access point or router just like I presume the desktop is already connected.  Astronaut (talk) 17:21, 5 March 2013 (UTC)

How can i check a large list of Radio buttons in 1 click?
i use firefox 19.0

any easy way for it? thx Ben-Natan (talk) 22:48, 3 March 2013 (UTC)


 * Radio buttons only require one click. Do you mean checkboxes? Pokajanje &#124; Talk  00:05, 4 March 2013 (UTC)
 * oh sorry, yes. ^_^ 79.183.98.234 (talk) 01:43, 4 March 2013 (UTC)
 * I'd suggest you use inject JavaScript! That's what it would be best, just type in the console  190.60.93.218 (talk) 13:22, 4 March 2013 (UTC)


 * If said checkboxes are right next to each other, you could also use the keyboard: Tab to move to the next checkbox, and spacebar to check/uncheck it. -- 143.85.199.242 (talk) 17:36, 4 March 2013 (UTC)

If jQuery is available:

→ Σ σ  ς. (Sigma) 23:07, 5 March 2013 (UTC)