In the context of Ethernets, what is the purpose of the synchronization preamble field from the beginning of an IEEE 802.3 frame? I'd take a guess that it was meant to distinguish packets from noise in the early days of the Internet. But why was it assigned a length of 7 bytes(more than the source/destination address fields)? Was the aim reliability?
In the IEEE 802.3 frame structure there is a 7 byte preamble section for synchronization. If it is really for synchronization does that mean Ethernet is synchronous and not asynchronous?    Ethernet structure for reference:
Minecraft Failed To Bind Port I made a server and used my IPv4 address for the IP. I decided to scratch that server and make a Bukkit server so I can use plugins. I tried to use my IPv4 address which I used for my other server but I keep getting the message [17:31:15 WARN]: ****FAILED TO BIND TO PORT!  Is there any thing I can do to get a new address to use or is there a way to delete the old server? Do I need to use a different computer? Please help! I've don't know how to fix this problem. If you have any suggestions please tell me and I'll give it a try. Let $f$ be a real valued, continuous and differentiable function on the real numbers with $f'$ uniformly continuous. Show that $g_n(x)$ with $$g_n(x)=nf(x+1/n)-nf(x)$$ is uniformly convergent to the derivative of $f$.   I cannot figure out how to solve this problem. If anyone could help me for this problem I would be very grateful. Do tag edits count for Archaeologist? How to recover deleted files? Reading quoted/escaped arguments correctly from a string ACPI PPC Probe failed. Starting version 219 NVIDIA I have 2 1tb hard drives on my computer with Windows 8 on the first hard drive and nothing on the other.  I want to install Ubuntu 14 on the second hard drive. I've looked up some guides and they all say to install Ubuntu on the sdb partition when booting off a usb stick. I have also seen some say to unplug the Windows HDD and then install Ubuntu onto the second HDD, and Ubuntu will automatically detect Windows and ask what you want to boot into upon boot.   I am really concerned about this - Will it ask me to choose what OS I want to boot into? Is there something like rEFInd(Mac) for Windows? Can anyone please give me a guide on how to do it without ruining my computer?  Thanks Why is it usually "friend of his", but no possessive apostrophe with "friend of Peter"? As  shows, we nearly always use the possessive form of personal pronouns for friend of mine/his/ours/etc.  But when it comes to actual names, we prefer  without the possessive apostrophe. That preference is even more marked with, say, . Not that I think the usage itself is particularly American - it's much the same with .  Personally, I find friend of him grates. In general I've no strong feelings either way as to whether it's friend of Peter or friend of Peter's (though I deplore the possessive in ), but in line with many others, I really don't like the possessive in relation to things like countries.  Why is this?   Edit: Noting an apparent "progression" (pronoun -> person -> nation) marked by reduction in use of the possessive, I checked at a finer "granularity". NGram shows that although it does occur,  virtually "flatlines" against friend of mine. But the bias reduces through of you, of us, and by the time I get to  it's much less extreme. There seems to be something "egocentric" about the double possessive.  Presumably when babies learn to speak, they soon notice that possessive pronouns, possessive apostrophes, and the word "of", all do the same job. Parents would correct a child who says "of mine's", but probably wouldn't even notice the same "redundancy" in "of Peter's". Younger speakers are unlikely to even be talking about something "of America's". Perhaps as we mature we tend to discard the "double possessive" for the more "distant" things that only adults are likely talk about, but we keep it for "closer" people because that's how we spoke when we were younger.  EDIT2 I note that I'm a great fan of him is vanishingly rare compared to ...fan of his, but with ...fan (of John) the double possessive occurs far less often than ...friend (of John's). Usage seems to be affected by the noun before "of" as well as the one after it. This is getting complicated... Recently I decided to use only Ubuntu and there is no Windows in my laptop. When I turn on my laptop the GRUB menu is showing but I don't need to choose OS anymore.   How can I remove or hide this? And after removing this how could I access to recovery mode? Proof for maximal ideals in $\mathbb{Z}[x]$ I have been trying to prove the following theorem:      Every maximal ideal in $\mathbb{Z}[x]$ has the form $(p, f(x))$ where $p$ is prime integer and $f$ is primitive integer polynomial that is irreducible modulo $p$.    Idea: I tried to establish a homomorphism $\phi: \mathbb{Z}[x] \rightarrow \mathbb{F}$. Since $\mathbb{F}$ is a field it has characteristic $p$ and so integer prime p are mapped to 0 in $\mathbb{F}$. Hence $p\in \ker \phi$. Next we consider $\phi': \mathbb{Z}[x] \rightarrow \mathbb{Z_p}[x]$ and pick an arbitrary maximal ideal $M\in \mathbb{Z}[x]$. So, $\phi'(M)$ is maximal as long as $p \in M$ by correspondence. But now I am stuck at this stage and do not know how to proceed. I guess we might have to use primitivity given in problem but dont know how. Often while playing Pathfinder, my group will run into problems where rules for 3-dimensional play simply don't exist, so far as we can find. Arguments will come up over things like carrying-capacity, movement speed, area-effects, and a variety of other things.  Simply put, are there rules for 3D play for Pathfinder, and if so where can I find them? Coordinating conjunction immediately followed by parenthetical — Is a comma needed or not? states:     If a dependent clause, or an introductory phrase requiring to be set off by a comma, precedes the second independent clause, no comma is needed after the conjunction.   Strunk's example illustrates the point:     The situation is perilous, but if we are prepared to act promptly, there is still one chance of escape.   However, I would be tempted to put a comma after the "but," like this:     The situation is perilous, but, if we are prepared to act promptly, there is still one chance of escape.   So, I know you're thinking, "Well, Strunk's Rules of Usage says that you're wrong. No comma."   But is Rules of Usage really the best source? I'd like to see this rule in a more contemporary and authoritative source, like the Chicago Manual of Style.  There are many instances —  — where the comma is included before a parenthetical comment that comes after a coordinating conjunction.  Any authoritative source on the issue? How do you pull first 100 characters of a string in PHP I had to take ownership of the special folder C:\Program Files\WindowsApps to fix . The issue is now resolved, so I'd like to reset the permissions to the way they were before I took ownership of the folder.  I reverted NT SERVICE\TrustedInstaller to the owner and removed my account's permission entries:     But I still have full control of the folder and can browse the folder in Explorer without getting the usual warning that I would have to take ownership:     Is it possible to restore the default permissions of this folder? Group of order 15 is abelian How do I prove group of order 15 is abelian?  Is there any general strategy to prove that a group of particular order(composite order) is abelian? Integrating $\int^{\infty}_0 e^{-x^2}\,dx$ using Feynman's parametrization trick How to prove $\,x^a-1 \mid x^b-1 \iff a\mid b$ How to prove $x^a-1\mid x^b-1 \iff a \mid b$, where $x \ge 2$ and $a,b,x \in \Bbb Z$.  I've tried the following in attempting to solve this:  $$a\mid b \Rightarrow aq=b \Rightarrow x^{aq}=x^b \Rightarrow x^ax^q=x^b$$  Because $x^q \in \Bbb Z$, it follows that $x^a\mid x^b$.  This is as far as I have gotten; any help getting further is appreciated.  Note: It may be that this identity is not true at all? What is inverse CDF Normal Distribution Formula Convert and redirect URL in uppercase to lowercase using .htaccess I would like to redirect a URL with uppercase characters http://localhost/A/B to a lowercase version http://localhost/a/b using the .htaccess file. Using regex I can capture A and B but is it possible to convert them to lowercase? How to prove $(f \circ\ g) ^{-1} = g^{-1} \circ\ f^{-1}$? (inverse of composition) I'm doing exercise on discrete mathematics and I'm stuck with question:     If $f:Y\to Z$ is an invertible function, and $g:X\to Y$ is an invertible function, then the inverse of the composition $(f \circ\ g)$ is given by $(f \circ\ g) ^{-1} = g^{-1} \circ\ f^{-1}$.   I've no idea how to prove this, please help me by give me some reference or hint to its solution.