E-mail & the Web
When someone checks e-mail, their software sends a username
(or mailbox name) and password to a server that might look something
like those shown here (many I.S.P.'s use multiple servers to
balance the load that can be placed on them at peak moments).
It figures out which of the thousands (or millions) of mailboxes
is theirs, and whether it contains anything, then responds accordingly.
All in a couple of seconds. Pretty amazing, when you really
think about it. But reliable access to e-mail is probably the
most important service an I.S.P. provides.
As for the World Wide Web, most of the sites you visit do not reside
on your I.S.P.'s servers, they merely provide you with connectivity
to them. Just the same, the I.S.P. likely has servers like the ones
shown here that contain the I.S.P.'s web site, and those of their users,
as well as any web hosting clients they might have. Thousands, if not
millions, of racks similar to the one shown exist all over the world,
and form the World Wide Web.
While, for many people, the Internet is just e-mail and the web, we
haven't seen the service that costs the most to provide: Usenet newsgroups.