Computer English Unit 9 The Internet（计算机英语 第九单元 因(4)

(identifying the Addison-Wesley domain) and the last byte (133) is the host address (identifying a particular computer within Addison-Wesley’s domain).

因此，位于艾迪生― 韦斯利（ Addison-Wesley ） 出版公司域内的一台计算机可能拥有192.207.177.133这个IP地址，其中前面的3个字节（192.207.177）构成网络标识符（标识Addison-Wesley这个域），最后一个字节（133）是主机地址（标识Addison-Wesley域内的一台特定计算机）。

Addresses in bit-pattern form (even when compressed using dotted decimal notation) are rarely conducive to human consumption. 用位模式形式表示的地址（即使经过使用点分十进制记数法压缩）很少能够有助于人们理解记忆。 For this reason each domain is also assigned a unique mnemonic address known as a domain name. 由于这个原因，每个域还分配了一个独特的助记地址，称为域名。

For example, the domain name of the Addison-Wesley publishing company is aw.com.

例如，艾迪生―韦斯利出版公司的域名是aw.com。 Note that the naming system reflects the domain’s classification, which in this case is commercial as indicated by the com suffix.

注意这个命名系统反映了域的分类。如后缀com所示，艾迪生―韦斯利出版公司的域属于商业性的。 Such classification is called a top-level domain (TLD).

这样的类别称为顶级域名。

There are numerous TLDs, including edu for educational institutions, gov for U.S. government institutions, org for nonprofit organizations, museumfor museums, info for unrestricted use, and net, which was originally intended for Internet service providers but is now used on a much broader scale.

顶级域名为数不少，包括表示教育机构的edu、表示美国政府机构的gov、表示非赢利机构的org、表示博物馆的museum、表示无限制使用的info以及net。net最初打算用于表示因特网服务提供商，但现在使用的范围要广泛得多。

In addition to these general TLDs, there are also two-letter TLDs for specific countries (called country-code TLDs) such as au for Australia and ca for Canada.

除了这些一般的顶级域名之外，还有用于表示具体国家的两字母顶级域名（称为国家代码顶级域名），如表示澳大利亚的au和表示加拿大的ca。

Once a domain has a mnemonic name, its local authority is free to extend it to obtain mnemonic manes for the machines within its domain. 一旦一个域拥有了一个助记名，其本地管理机构就可自由地扩展该助记名，从而为域内的计算机取得助记名。

For example, an individual machine within the domain

aw.com

might

be

identified

as

ssenterprise.aw.com.

例如， 位于aw.com 域内的一台计算机可能被标识为ssenterprise.aw.com。

We should emphasize that the dotted notation used in mnemonic addresses is not related to the dotted

decimal notation used to represent IP addresses. 应该强调的是，用于助记地址的点分表示法与用于表示IP地址的点分十进制记数法没有关系。

Instead, the sections in a mnemonic address identify the computer’s location within a hierarchical classification system.

相反，助记地址的各部分标识计算机在一个层次分类系统中的位置。

In particular, the address ssenterprise.aw.com indicates that the computer known as ssenterprise is within the institution aw within the class (or TLD) of commercial domain com.

具体来说，ssenterprise.aw.com这个地址表示：称为ssenterprise的计算机位于aw这个机构内，而aw则属于com这个商业性域类（或顶级域名）。

In the case of large domains, a local authority might break its domain in to subdomains, in which case the mnemonic addresses of the computers within the domain might be longer. For example, suppose Nowhere University was assigned the domain name nowhereu. edu and chose to divide its

domain into subdomains.

在大型域的情况下，本地管理机构可能将其域分成子域。在这种情况下，域中计算机的助记地址可能比较长。

Then, a computer at Nowhere University could have an address such as r2d2.compsc.nowhereu.edu, meaning that the computer r2d2 is in the subdomain compsc within the domain nowhereu within the class of educational domains edu.

例如，假设乌有大学被赋予nowhereu.edu这个域名，并选择将其域分成子域。那么，乌有大学的一台计算机就可能具有像r2d2.compsc.nowhereu.edu这样的一个地址。该地址表示：称为r2d2的计算机位于子域compsc中，而子域compsc则在nowhereu这个域中，而nowhereu这个域又属于edu这个教育性域类。

Each domain’s local authority is responsible for maintaining a directory containing the mnemonic address and the corresponding IP address of those computers within its domain.

每个域的本地管理机构负责维持一个目录，里面含有该域中每台计算机的助记地址和相应的IP地址。