Netnews, or Usenet as it is more commonly called, is a message sharing system that exchanges messages electronically around the world in a standard format. Messages exchanged on Usenet are arranged by topic into categories called newsgroups. Netnews is, thus, a huge collection of messages, being passed from machine to machine. The messages may contain both plain text and encoded binary information. The messages also contain header lines that define who the message came from, when the message was posted, where it was posted, where it has passed, and other administrative information.
The major, hierarchical categories of Usenet newsgroups which are distributed throughout the world are alt, comp, misc, news, rec, sci, soc, and talk. There are many other major categories which may be topical (eg, bionet, biz, vmsnet) and are usually distributed worldwide as well, or geographical and even organizational (eg, ieee) or commercial (eg, clari). The latter categories are usually distributed only with their area of interest. The messages of many Bitnet LISTSERV mailing lists are also distributed in Usenet under the major category bit.
The major categories are further broken down into more than 1200 newsgroups on different subjects which range from education for the disabled to Star Trek and from environmental science to politics in the former Soviet Union. The quality of the discussion in newsgroups is not guaranteed to be high. Some newsgroups have a moderator who scans the messages for the group before they are distributed and decides which ones are appropriate for distribution.
Usenet was originally developed for Unix systems in 1979. Within a year, fifty Unix sites were participating. Now, there are thousands of sites running a number of operating systems on a variety of hardware platforms communicating via Usenet around the globe.