A newsgroup begins on a single news server, but is eventually replicated to hundreds or thousands of other servers. News servers provide the infrastructure that makes newsgroups work. Each news server has special software that maintains a file for each newsgroup serviced by that server.
Here's what happens when you access a newsgroup:
- Your newsreader, using NNTP, connects to the news server designated in your configuration. Typically, the news server's connection information is provided to you by your Internet Service Provider (ISP). If your ISP does not have a news server, you can refer to a list of publicly accessible news servers.
- Once the connection is established, your newsreader downloads all of the new messages posted in the newsgroups that you are subscribed to.
- Your newsreader sends your messages to the news server. (If it's an offline newsreader, it must first reconnect to the news server via NNTP).
- The news server saves your messages in the file for that newsgroup. Newsgroup files are large text files, meaning that each new message is simply appended to the end of the text file. As the file reaches a certain size, or after a certain length of time, the messages at the beginning of the file are removed and placed in a newsgroup-archive text file.
- The news server connects to one or more other news servers using NNTP (or UUCP) and sends the updated information. Each news server compares its own file for the newsgroup with the files it receives for that same newsgroup. It adds any differences that it finds -- this is important, because if the news server simply saved the received file over the one it already had, it would lose any messages posted to it during the update. By comparing the files, it can extract the new messages and add them to the file it has, without losing any new postings. The news server then sends the combined file to the other news servers.
- The newsgroup changes are replicated to each news server until all of them have the updated information. This process is ongoing, and most large newsgroups change so quickly that the updating is virtually continuous.
- Other subscribers read your messages, plus all the others posted since the last time they looked at the newsgroup, and reply.
- You see their replies and new messages, and the process repeats.