Wikipedia:Reference desk/Archives/Computing/2015 July 8

= July 8 =

L1 and L2 cache
Do I understand correctly? Does L1 cache generally equals "CPU cache" and L2 generally equals "RAM"? if so, what is L3 than? Ben. Ben-Yeudith (talk) 01:03, 8 July 2015 (UTC)
 * No. With modern CPU architectures, all Lx caches are on the CPU, just different hierarchies. See CPU cache for more. Older CPU architectures (like 20 years ago or so), had external caches, but these were still distinct from normal RAM (system memory). AFAIK, all CPU caches whatever the hierarchy and location can be considered a type of RAM. Nil Einne (talk) 03:11, 8 July 2015 (UTC)
 * Nice to know that... So if we say the Memcache software of servers creates a RAM memory cache the real meaning is it actually a CPU cache based caching? Ben-Yeudith (talk) 09:15, 8 July 2015 (UTC)
 * If you are talking about Memcached, that's something completely different from a CPU cache. --Guy Macon (talk) 09:58, 8 July 2015 (UTC)


 * I have a Drupal site and In my Cpanel I use Memcache to build cache on the RAM... in relation to what User:Nil Einne wrote, I ask what type of memory this? the Memcached article speaks about RAM, or it different than what I think. Ben-Yeudith (talk) 11:30, 8 July 2015 (UTC)


 * OK. I understand the question. This has absolutely nothing to do with LI, L2 or L3 cache. They share the name "cache" but its like the difference between being "next in line" for a teller at your local bank and being "next in line" for the throne when the Queen of England dies. Completely different concepts. The memcache you configure using cpanel is just ordinary RAM on the web server, used in a clever way to make high volume websites faster.


 * Here is the best explanation I know of Drupal caching: https://openconcept.ca/blog/mmallett/apc-varnish-memcache-and-caching-beyond-drupal-core


 * In the Drupal context, everything called "caching" is simply ordinary reads and writes to RAM. Caching info in RAM and retrieving it later can be used to avoid having to get the info from disk, or it can be used to avoid asking another server for the info. --Guy Macon (talk) 12:54, 8 July 2015 (UTC)


 * Why would Memcached won't use the CPUcache? Isn't it preferable from the regular RAM cards? Ben. Ben-Yeudith (talk) 09:17, 9 July 2015 (UTC)


 * CPU cache is tiny and fast. It's used by the operating system to keep tiny things easily accessible for what would seem to a human person like tiny periods of time. Programs can't access it. So sure, it's preferable, in the same way a bullet is preferable to a 747. Bullets are very small and very fast, but you wouldn't ride one across the Atlantic. —Noiratsi (talk) 11:46, 9 July 2015 (UTC)


 * Programs generally have no control over the CPU cache. It's "invisible" to software; the CPU moves data in and out of cache automatically. I highly recommend that anyone interested in computers read this series of articles by Ulrich Drepper (former lead maintainer of glibc) about how computer memory works. Fair warning: it's a bit dense, and will take some time to get through, but you will learn a lot. --108.38.204.15 (talk) 14:21, 9 July 2015 (UTC)

Where do you report grammatical errors?
These are the errors.

Type Walter Mercado and see that there is a mistake in the first section of the article - "early years". The mistake is:"He also studied singing had a talent for dancing." Another mistake is on the Ilana Kratysh article in the "early and personal life" section, where it says "and she often attends synagogue.". — Preceding unsigned comment added by 65.88.88.17 (talk) 04:12, 8 July 2015 (UTC)
 * You don't need to "report" it. "This is Wikipedia, the encyclopedia that anyone can edit."  Almost true; true enough for your purposes anyway.  Find the relevant section, click on the blue [edit] link, make your fix, add an edit summary, and hit "save". --Trovatore (talk) 04:16, 8 July 2015 (UTC)


 * If you'd rather not correct it yourself, every article has a Talk page, which is easier to find than this page and more likely to be read by someone who cares about the article. —Tamfang (talk) 08:49, 10 July 2015 (UTC)

New pages
Hi

I am a Computer Science student and often refer to Wikipedia before going else where to find information for assignments etc. There are a few areas I have searched for recently which do not seem to exist on Wikipedia so I am interested in writing some content to help others.

Are there any hard and fast rules I should abide by? To avoid my pages being removed or deleted for example after hours of work?

Many Thanks Joanne — Preceding unsigned comment added by 86.140.255.99 (talk) 09:35, 8 July 2015 (UTC)
 * Have a look on Help:Contents: that should tell you all you need to know.--Phil Holmes (talk) 10:07, 8 July 2015 (UTC)


 * It seems unlikely that any area of Computer Science you've come across in an assignment is not already covered in depth on Wikipedia. Make sure to search carefully. Maybe you could tell us what information you couldn't find? The people on this helpdesk will certainly know where to look to see if we already have an article on it. —Noiratsi (talk) 18:48, 8 July 2015 (UTC)

Write PHP multiple picture upload and database storage code for me
How to upload multiple picture at a time using php and mysql and save the url's of the images with seperator along with form data in the database ?106.51.131.180 (talk) 12:31, 8 July 2015 (UTC)

Could our Quickbooks connectivity issues be caused by our network setup?
Hello,

I am an employee in a small business. We have a server machine that has our Quickbooks company file on it, which we connect to with other computers that have Quickbooks. Our computers are actually all connected together using a firewall, "Netgear ProSafe FVS318N".

We have had continual issues with losing connection to the server on all our machines. This would happen seemingly randomly. An error message would come up saying something like "ABORT: Quickbooks has lost connection to the company file", although this may not be the exact message. We have gone back and forth speculating what the cause of this may be. Most of our computers are using Windows 7 or Windows 8. The "Server" machine is Windows 7.

My co-workers explain to me that they had experienced much less issue with connectivity when we were using Windows XP, and that the issue is related to either our version of QB, or some incompatibility with QB and the "newer" windows operating systems. (We are using Quickbooks Enterprise, manufacturing and wholesale 14.0)

I personally don't think this makes any sense, and rather look to our network configuration, although i am a novice with regard to knowledge of networking and its devices. Why do we have a firewall as the center of our network? Since the clients appear to randomly drop connection with the server's Quickbooks database, wouldn't one be able to say it is because a firewall generally blocks all ports of communication unless you write special rules to let this or that one through?

Is it possible that i am correct, and that by switching to a Network Switch instead of a Firewall device, we may enjoy longer periods of using QuickBooks without interruption? Is there possibly something else going on here that i don't understand?

Thanks in advance for all help and advice!

216.173.144.188 (talk) 14:41, 8 July 2015 (UTC)


 * The NetGear ProSafe did have connection drop issues with VPN. I doubt you are using VPN inside your office. A firmware update fixed those issues. Are you running the latest firmware? If not, it is a good idea to update it. Then, are you running open wireless access to the switch/firewall with the default admin password? If so, it would be trivial for someone nearby to be using your network and, whenever they like, kick people off the switch. 209.149.114.69 (talk) 18:12, 8 July 2015 (UTC)


 * We have not been using the VPN style setup on the firewall. We do have wireless communication set up, but we are not using the default credentials. We will try to update the firmware anyway. You are saying its perfectly normal for a company to operate with a firewall connecting all devices, instead of a switch? If that is so, i wonder if it does have to do with incompatibility with new windows versions, or perhaps an EMF from the lights on the wires or something like this.


 * 216.173.144.188 (talk) 18:27, 8 July 2015 (UTC)


 * Internally, it is just a switch. It is not a firewall. The firewall is between the external/wan port and the internal switch. So, all 8 of the ports that you can physically plug into transfer between one another without any hint of a firewall. Further, you will see it is set up in two sets of 4. Any communication to a port in one set of four is sent to all four. They broke it into two sets of four to call it a switch instead of a hub. It is really just two hubs. The wireless access is completely different. It is wireless N if memory serves. You could be getting high interference on the wireless connection, causing disconnections. So, the first step is to identify if a computer hard-wired into the switch also has the disconnect problem. If not, you have limited the problem to wireless connected computers. That is most likely interference. Many things cause WiFi interference: walls, microwaves, bluetooth devices, other wifi devices, UFOs, etc... 209.149.114.69 (talk) 19:11, 8 July 2015 (UTC)
 * Yeah, we get a lot of problems with UFOs ... — Preceding unsigned comment added by 109.153.232.72 (talk) 00:07, 9 July 2015 (UTC)