Some companies maintain a network that is linked to the Internet via dedicated communication lines.
Those with less substantial resources, including most individuals, access the Internet via a service provider. A service provider is a company that offers use of its dedicated communication lines. If you have a modem, you can dial up a service provider whose computers will connect you to the Internet, typically for a fee. Dial-up access means that the modem on your computer can log in to another computer that is hooked up to the Internet. When using a shell account, you dial into a service provider's computer and use the UNIX operating system to indirectly connect to the Internet.