Unix-to-Unix Copy (UUCP) started out as a package of programs that transferred files over serial lines, scheduled those transfers, and initiated execution of programs on remote sites. It has undergone major changes since its first implementation in the late seventies, but it is still rather spartan in the services it offers. Its main application is still in Wide Area Networks, based on periodic dialup telephone links.
UUCP was first developed by Bell Laboratories in 1977 for communication between their Unix development sites. In mid-1978, this network already connected over 80 sites. It was running email as an application, as well as remote printing. However, the system's central use was in distributing new software and bug fixes. Today, UUCP is not confined solely to the Unix environment. There are free and commercial ports available for a variety of platforms, including AmigaOS, DOS, and Atari's TOS.
One of the main disadvantages of UUCP networks is that they operate in batches. Rather than having a permanent connection established between hosts, it uses temporary connections. A UUCP host machine might dial in to another UUCP host only once a day, and then only for a short period of time. While it is connected, it will transfer all of the news, email, and files that have been queued, and then disconnect. It is this queuing that limits the sorts of applications that UUCP can be applied to. In the case of email, a user may prepare an email message and post it. The message will stay queued on the UUCP host machine until it dials in to another UUCP host to transfer the message. This is fine for network services such as email, but is no use at all for services such as rlogin.
Despite these limitations, there are still many UUCP networks operating all over the world, run mainly by hobbyists, which offer private users network access at reasonable prices. The main reason for the longtime popularity of UUCP was that it was very cheap compared to having your computer directly connected to the Internet. To make your computer a UUCP node, all you needed was a modem, a working UUCP implementation, and another UUCP node that was willing to feed you mail and news. Many people were prepared to provide UUCP feeds to individuals because such connections didn't place much demand on their existing network.
We cover the configuration of UUCP in a chapter of its own later in the book, but we won't focus on it too heavily, as it's being replaced rapidly with TCP/IP, now that cheap Internet access has become commonly available in most parts of the world.