A short time after people started utilizing Usenet as an all-text discussion forum, the users of certain newsgroups thought that this system would be ideal to share files with each other. However, the newsgroups were not designed to transfer binary files – they could only transfer text files. Users then thought of taking a binary file and converting it (encoding it) so that it is becomes a text message. That enabled users to distribute those text messages (containing files) throughout the newsgroups in Usenet, and then whoever wanted the file, could just download the message and convert it back (decode it) into the original binary file.
The newsgroups operate in almost the same way today. Of course, there have been great improvements in the software used to download the messages from the news server to the individual’s computer that makes getting files from the newsgroups a lot easier than it was in the beginning.
A typical large file from a binary newsgroup is usually split into many pieces, as there is a limit to the file size that can be inserted in a text message. Many news servers will not accept messages that are longer than 10,000 lines, many even less than that.
That is why files need to be split up in many parts and each part needs to be posted separately on the server. Programs like WinZIP and WinRAR can split files in equal parts (and a reminder) for you. The RAR/ZIP files are then split into text messages, each one containing the maximum number of lines (or less). These are then posted to the newsgroup. It may sound complicated but it is actually a very efficient way to post large files, spreading them out in different articles. Similarly, the messages can be downloaded and put back together by newsreaders in the same manner, resulting in the original file that was posted.