简介（Introduction）

When deciding which server architecture to use for your environment, there are many factors to consider, such as performance, scalability, availability, reliability, cost, and ease of management.
Here is a list of commonly used server setups, with a short description of each, including pros and cons. Keep in mind that all of the concepts covered here can be used in various combinations with one another, and that every environment has different requirements, so there is no single, correct configuration.

TCP的报文结构（TCP segment structure）

basic structure

Interactive applications,however, often transmit data chunks that are smaller than the MSS; for example, with remote login applications like Telnet, the data field in the TCP segment is often only one byte. Because the TCP header is typically 20 bytes (12 bytes more than the UDP header), segments sent by Telnet may be only 21 bytes in length. Figure bellow shows the structure of the TCP segment.

好的交互设计可以区分开有质量的网站和其他普通网站。然而，如果有明显的设计错误，它只会给予你本来想打动的用户以刺激和挫败感。下面是Speckyboy上总结的让人最不喜欢的交互设计错误列表，来看看你中枪了没！
Interaction design can separate the quality sites from the rest of the crowd – if done well. If, however, there are glaring errors in the designs, it will only serve to irritate and frustrate the very people you’re trying to impress.
Here’s a list of my least favorite IxD mistakes that have left users disappointed, confused, and can even at times leave them a little angry.

缺乏对比（Lack of Contrast）

译文：当浏览网站时，我们喜欢看页面设计展示出干净、清爽的对比。对比达到了一个重要的目的——它使内容可读，并毫不费力地在页面上指导用户。这是一个最基本的设计概念，只是很奇怪，有些网站似乎就是不明白。
没有足够的对比度的话，不管是颜色或整体展示，一个网站看起来，在最好的情况下，也会让你觉得有点儿丈二和尚摸不着头脑，在最坏的情况下，将会使页面完全不可读。

“用户的期望更多地被证实是正确的,他们就会越觉得他们在控制系统,并会更加喜欢它。”
雅各布·尼尔森

Summary: Jakob Nielsen’s 10 general principles for interaction design. They are called “heuristics” because they are broad rules of thumb and not specific usability guidelines.

Visibility of system status

The system should always keep users informed about what is going on, through appropriate feedback within reasonable time.

Match between system and the real world

The system should speak the users’ language, with words, phrases and concepts familiar to the user, rather than system-oriented terms. Follow real-world conventions, making information appear in a natural and logical order.

密钥生成随机选择两个不相等的质数p和q。例子中选择了7和11。（实际应用中，这两个质数越大，就越难破解。） 计算p和q的乘积n。 n = 7×11 = 77 n的长度就是密钥长度。77写成二进制是1001101，一共有7位，所以这个密钥就是7位。实际应用中，RSA密钥一般是1024位，重要场合则 ...

质（素）数（Prime Number）

定义：大于 1 且只能被 1 和自身整除的正整数称为素数或质数. 大于 1 且不是素数的正整数称为合数.
例如, 2,3,5,7,11是素数, 4,6,8,9是合数.
一个好玩的现象，如果将所有素数进行螺旋排列，所有素数呈现斐波那契螺旋线排列，在计算机下的模拟如下：