Wikipedia:Reference desk/Archives/Computing/2010 September 10

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September 10

Using optical drive ports for hard drives?

Many consumer level desktops are currently laid out with the expectation of 1 or 2 hard drives (possibly using RAID 0 or 1) and 1 or 2 optical drives. Is it feasible in general to use one of the optical drive connections for an additional hard drive? If so, what limitations are there in such an approach? For example, does the optical drive connection have a lower bandwidth than the normal hard drive connection? Dragons flight (talk) 03:54, 10 September 2010 (UTC)

They're identical. New desktop computers use SATA cables for both hard drives and optical drives. Older computers used PATA cables for both.--Best Dog Ever (talk) 04:17, 10 September 2010 (UTC)

A lot of motherboards in the last few years still had a single PATA connector which we use a lot to connect older CD/DVD drives, whilst using the SATA connector for the harddisks. (No sense in replacing all those (rarely used anyway) optical drives with SATA ones) Unilynx (talk) 06:56, 10 September 2010 (UTC)

But in his case, if the cables look the same, then they are the same. If one is a ribbon cable and the other is a thin cable, then they aren't the same.

I prefer SATA over PATA optical drives because ribbon cables restrict airflow inside the case. It's also been my experience that PATA optical drives cause the computer to lock up while the drive reads a disk.--Best Dog Ever (talk) 07:12, 10 September 2010 (UTC)

Using another type of wiki

During the introduction to my first grad school class (last week), my professor told us that we'd be making some presentations on a class-only wiki. I was excited, of course, but my excitement dropped after I found that it didn't run MediaWiki — the engine is something called "Radeox", and it appears that it's written in Java. I've googled the term, but the most that I can find is this blog that appears somehow to be associated with it. List of wiki software doesn't say anything about it.

Is anyone familiar with using this type of engine? I've discovered that it doesn't have many MediaWiki features — there are no templates, equals signs don't produce headers, links are made [like this] rather than [[like this]], and typing ~~~~ and saving produces a text of ~~~~. I believe that I can get around these missing bits, but I can't find the watchlist — if you know how to use this software, how do I find the watchlist? I know that there is one, because the software tells me that I can watch pages, although it doesn't tell me how to view the watchlist. Nyttend (talk) 05:13, 10 September 2010 (UTC)

I think you'll find that the markup renderer is a component of the actual wiki software, which will be in charge of watchlists and such. Similar to how the WebKit HTML renderer is used in multiple browsers. My advice would be to focus on the content of the class and/or wiki and not on the (lame-sounding) infrastructure that's there. --Sean 13:43, 10 September 2010 (UTC)

Internet speed, difference between 1 mb/s and 6 mb/s?

Currently my internet speed is 6 mb/s, but I am rarely able to use it to it's potential. I usually download files from megaupload, and the speed is 0.7 mb/s. I am thinking about switching to cheaper internet. Since I'm only downloading at 0.7 mb/s, a 1 mb/s internet connection would be just as good, right? Or is it more complicated? Thanks.--69.135.164.206 (talk) 05:35, 10 September 2010 (UTC)

What do you use to download files? Internet Explorer displays downloading speed in megabytes per second (MBps) and ISPs advertise in megabits per second (mbps). There are 8 bits in a byte:

0.7 MBps x 8 bits/byte = 5.6 Mbps

And if you were rounding down to 0.7, this is what you have:

0.75 MBps x 8 bits/byte = 6 Mbps

Does that make sense?--Best Dog Ever (talk) 06:31, 10 September 2010 (UTC)

To summarise what Best Dog Ever said, you're actually getting very very close to what you should be getting. 6 Mbps = 0.75 MBps. This bit/byte problem is a very common misconception which ISPs seem averse to dispelling. For example, if you were to switch to a 1 Mbps service, you would end up with a maximum speed of around 0.125 MBps, so this wouldn't be in your best interests. Regards, Brammers (talk/c) 07:26, 10 September 2010 (UTC)

There are 8 bits in a byte, and 1,000,000 bits in a megabit. But as displayed by Internet Explorer, there are 1,048,576 bytes in a megabyte. This means 1 megabyte = 8.388608 megabits and 0.7 megabytes per second is about 5.87 megabits per second. So you are getting close to what you're paying for. --Bavi H (talk) 01:43, 11 September 2010 (UTC)

IIRC megabit per second is abbreviated as mbps, while megabyte per second is abbreviated as mBps. This is also true with kilobit/kilobyte (kbps/kBps). The difference is the capitalized letter B. You should check it carefully. But it seems that these 2 abbreviations are often used synonymously. -- Livy the pixie (talk) 14:47, 12 September 2010 (UTC)

That makes sense! I've always wondered why I download so slow. Thanks for clarifying.--69.135.164.206 (talk) 19:29, 12 September 2010 (UTC)

Other than IP Address, how else do forums/Q&A sites, etc. know that you're the same person?

Years ago, on an IGN forum, after I logged off and got a new IP address, I posted under a new account (with a different registration email of course) and asked one of the mods if they knew who I used to be.

The reply was, "You're (old username), right? IPs don't matter..."

So what other methods do they use to know that you're the same person? Please be as comprehensive as you can. Thanks. --70.179.165.170 (talk) 10:58, 10 September 2010 (UTC)

Chatted about this in IRC, a bit; I mentioned cookies, User agent, Anon proxies and suchlike - and emphasized that Wikipedia does not permit the latter, of course.  Chzz  ►  11:14, 10 September 2010 (UTC)

Clarification: Wikipedia doesn't permit editing from open proxies. You can read Wikipedia from an open proxy as much as you'd like. Comet Tuttle (talk) 15:16, 10 September 2010 (UTC)

Further clarification: Users are allowed to edit from open proxies, but the proxies may be blocked at any time. "legitimate users ... are not the intended targets and may freely use proxies until those are blocked". Wikipedia:Open proxies 82.44.55.25 (talk) 15:30, 10 September 2010 (UTC)

If your method of getting a new IP address involved something like rebooting your router, you would have been allocated another address in the same block. It's not rocket science, given a new user who is suggesting they used to be someone else, to look up other users from similar IP addresses. Marnanel (talk) 12:08, 10 September 2010 (UTC)

Your new ip was probably similar to the old one. They geolocate it and it goes to the same country / city etc, it's probably you. Also maybe they recognized your style Quadrupedaldiprotodont (talk) 14:37, 10 September 2010 (UTC)

sub-question

Has anyone heard of internet servers that attempt to identify by MAC address? I realize there are all kinds of inherent issues with that, but it would not surprise me if a last-ditch effort was made by an advertising server, for example, to tie a MAC address (or just the IP, for that matter) to a previously established cookie-based profile. I hope this makes sense. In practical terms, I delete cookies with every browser close: I would think ad servers would be motivated enough to come up with other ways to tie my browsing session to an existing profile by my IP or even MAC address. Riggr Mortis (talk) 22:12, 10 September 2010 (UTC)

The MAC address is a link-local address. It's only transmitted in ethernet packets for a single hop (depending on your network configuration, either to your gateway or to your ISP's router). From there IP packets are reencapsulated in different ethernet frames (or other kinds of low-level frames, such as SS7 or ATM frames). So no, at most only your ISP sees your MAC; it's not sent over The Internet proper, and thus isn't available to websites etc. for tracking you. -- Finlay McWalter ☻ Talk 22:22, 10 September 2010 (UTC)

With normal DSL broadband links, the MAC address gets no further than your DSL modem/router. --Phil Holmes (talk) 10:37, 11 September 2010 (UTC)

Wouldn't that device have its own MAC address, though? Excuse my ignorance, just wondering. I'm sure some device I used to own had a little sticker on it which said something like "MAC 01:23:45:67:89:ab", and I think it was a cable modem. 81.131.17.37 (talk) 11:38, 11 September 2010 (UTC)

That's good to know, I figured my question was probably ill-informed and I was right! Riggr Mortis (talk) 22:28, 10 September 2010 (UTC)

However, IPv6 does, in its standard configuration, use the mac address to create an IPv6 address, which would allow such tracking. Fortunately, Ipv6 also has a privacy option which allows it to use temporary addresses for outbound connections. Unilynx (talk) 00:30, 11 September 2010 (UTC)

Note that some programs do use your MAC address for tracking (along with a host of other things) particularly free non browser online games more particularly the anti-cheat programs that come with them. America's Army is one that I know that does but I'm pretty sure it's not the only one. This shouldn't be that surprising, any program that runs on your computer is able to send whatever info it can gather from your computer to whatever server you allow it to communicate with, the good ones will mention in their EULA or whatever Nil Einne (talk) 09:42, 12 September 2010 (UTC)

Hard drives

Are hard drives becoming more reliable over time, or are drives from 1987 just as reliable as modern drives? —Preceding unsigned comment added by Overdowner (talk • contribs) 13:57, 10 September 2010 (UTC)

I would think more modern hard drives are more energy efficient and reliable, at least certainly more energy efficient. There's a bit more information here. Chevymontecarlo - alt 15:59, 10 September 2010 (UTC)

Are you asking how a new hard drive from 1987 would compare to a new modern drive, or are you asking if you should replace the 23 year old relic that you're storing your tax documents on? Because if it's the latter, I think anyone would say "yes, of course, after 23 years of use that thing is long past due to fail" (even modern hard drives last what, 5 years?). If it's the former question, than I don't know. Buddy431 (talk) 01:20, 11 September 2010 (UTC)

The unrecoverable error rate of modern harddrives are atleast two (possibly three?) orders of magnitude better than 1987 harddrives. So atleast in terms of data integrity, modern harddrives are much more reliable. Plus, AFAIK, the annualized failure rate of modern harddrives is much lower than 1987 harddrives. Rocketshiporion♫ 02:22, 11 September 2010 (UTC)

Almost certainly phishing email, but top-level domain is paypal.com

Resolved

 – $\sim$ Lenoxus " * "

Received a message consisting the following very suspicious text:

Dear customer, Your account has been temporarily limited. Download and fill out the form to resolve the problem. Thank You.

Message is from 'PayPal Inc. <notice@personal.paypal.com>'. Message's 1 attachment is the "form" in question, which looks to be some sort of HTML file, or URL file (whatever those are called).

Simple Googling of the phrase "Your account has been temporarily limited" indicates that it's almost certainly not a phrase PayPal uses, so I'm looking at a scam. (On top of that, they don't use the name of the account holder (just "Dear customer"), and if the real PayPal needed information, there would be a link to their site.)

So what I'm wondering is, how are the scammers able to use the top-level domain paypal.com? As far as I can tell, it's not an IDN homograph attack. Using Wikipedia, each of the letters seems to check out. Is it possible that when I copy the address in mail.app, the application actually "substitutes" the Latin characters and sends those to the clipboard? Or is there some scary way that phishers can disguise their address to look exactly like that of anyone in the world, without having to take over that person's computer (which I doubt has happened to PayPal)? $\sim$ Lenoxus " * " 14:51, 10 September 2010 (UTC)

It sounds like an HTML email (that is, an email where the content is in essence coded like a web page) where links are constructed to appear to go to paypal.com, but if you actually were to click on them (which I don't recommend at all) you'd really go to something fake. Hover over the links in Wikipedia:Phishing e-mails to see an example of how this appears. -- Finlay McWalter ☻ Talk 15:01, 10 September 2010 (UTC)

(ec) Sorry, I'm not clear on one part of your question. Is the "paypal.com" you're referring to in the "From" field of the e-mail, or are you referring to an apparent "paypal.com" URL within the HTML file somewhere? If the former, I would assume the "paypal.com" in the e-mail's "From" field is simply forged — it is trivial to do this — and the actual attack is to get you to open a malformed HTML file that targets old browsers. Comet Tuttle (talk) 15:02, 10 September 2010 (UTC)

To echo Comet Tuttle, where does the HTML attachment point to (you can download it and open it in Notepad for example)? I think the trick is to get you to click on the attachment, which would naturally open your browser and take you to the linked shortcut. It is trivial to forge the "from" address (or any other field) to reflect the actual, real paypal.com TLD. Email is an unsecure, plain-text standard. Zunaid 15:09, 10 September 2010 (UTC)

Remember that the "From" address on an email can be easily forged. Very easily. APL (talk) 15:24, 10 September 2010 (UTC)

Thanks for all the answers! Yes, I was curious about whether the "From" part, which does say "paypal.com" in Latin letters, could be forged. That's scary! $\sim$ Lenoxus " * " 16:10, 10 September 2010 (UTC)

See our article section E-mail#Header fields for more detail on the e-mail headers. Comet Tuttle (talk) 17:09, 10 September 2010 (UTC)

E-mail "from" headers are easily forged; don't trust those at all. --Mr.98 (talk) 17:11, 10 September 2010 (UTC)

Data compression built into TCP/IP

In the latter days of dial-up modems, the V.42bis spec had the modems actually perform Lempel-Ziv compression upon data before sending it over the wire. Nowadays, when I'm looking at web sites or using FTP with my nice Ethernet rig over a cable modem or DSL, is there any data compression going on between my computer and the servers it contacts? I mean to ask this question broadly; I don't want to restrict the question literally to TCP/IP, but want to learn about data compression taking place at any stage of the communication between the computers. Whether there is or not, I'd love pointers to any articles or books discussing the compromises involved and why the decisions were reached. Comet Tuttle (talk) 15:12, 10 September 2010 (UTC)

There is optional compression (e.g. CCP, MPPC) in the PPP layer; I don't know whether, in practice, the PPPoE and PPPoA systems used for delivering broadband internet to home users actually bother with this. There is optional gzip compression in the HTTP layer (details). PPTP can, I think, use the same compression schemes as PPP. -- Finlay McWalter ☻ Talk 15:23, 10 September 2010 (UTC)

I do not believe that, as a general rule, the servers and routers in the internet do any compression at all. Of course, the exception to this would be to state the obvious that JPEG, MPEG, MP3, etc., are all heavily compressed formats. Given the compression that's already applied to most large datasets, such as these, it would probably be a waste of processing power and intellectual effort to try compressing internet data. --Phil Holmes (talk) 16:54, 10 September 2010 (UTC)

@Phil...no there is compression with HTTP ussually using gzip. See HTTP compression. SSL can also use Lempel-Ziv-Stac (LZS) compression. Hope this helps.Smallman12q (talk) 20:42, 10 September 2010 (UTC)

All major web servers (e.g. Apache) and many web publishing platforms (e.g. Mediawiki) have built-in support to exploit the optional gzip compression over HTTP when web browsers acknowledge support for that compression (which is true for all major browsers). The web site operator may have to turn on these features, but the burden for doing so is generally small, which allows gzip over HTTP to be widely used. Dragons flight (talk) 21:16, 10 September 2010 (UTC)

It is often the job of a network engineer to decide whether CPU-time (or dedicated DSP calculation time) is cheaper or more expensive than network bandwidth. When the tradeoff is good (i.e., computing the compression is cheaper than sending the data uncompressed), the engineer will opt to use a compression system. I think this is often the case in large "internet backbone" scale data transfers; but in most point-to-point (read: last mile) connections, CPU is proportionately more expensive than bandwidth, so data is not compressed. Nimur (talk) 15:19, 12 September 2010 (UTC)