Each computer on the Internet has one or more Internet addresses, numbers which identify that computer among all those on the Internet. Users typically write numeric host addresses as sequences of four numbers, separated by periods, as in `128.52.46.32'.
Each computer also has one or more host names, which are strings of words separated by periods, as in `churchy.gnu.ai.mit.edu'.
Programs that let the user specify a host typically accept both numeric addresses and host names. But the program needs a numeric address to open a connection; to use a host name, you must convert it to the numeric address it stands for.
| Abstract Host Addresses | What a host number consists of. |
| Data type | Data type for a host number. |
| Functions | Functions to operate on them. |
| Names | Translating host names to host numbers. |