Usenet newsgroups were originally designed with the idea that only a few small text articles would be posted each month. As is often the case, the inventors of the technology had no idea what people would eventually do with it. And because of this design limitation, sometimes things don’t work smoothly. One of the things that can go wrong is ‘propagation.’
Just about every ISP has a news server. So, if you post something to your ISP’s server, it then has to propagate to all the other news servers in the world. The servers are all linked together, and propagation usually is very rapid, often taking only seconds. However, there are many things that can go wrong. News servers require gigantic arrays of hard disks to hold all the files that people are constantly posting – a load which never stops growing. There is also the constant war against spam, along with hardware failures, software bugs, and guys with backhoes cutting cables.
Since a large file must be posted in hundreds or thousands of pieces, it is common for a news server to be missing some of those pieces since each post must travel across the internet independently – unless the person posting it is a customer of the same ISP as you are. In that case, you will rarely see any missing parts.
The use of PAR files has greatly reduced this problem since they can magically re-create missing posts. However, not everybody knows how to make PAR’s, and you will often find that you can’t download a file because some parts are missing. So, in addition to your ISP’s news server, you will want to have an account with a third-party news service such as Easynews. With access to two servers, you will usually be able to find all the parts.
Having access to more than one news server is also handy because no ISP or NSP is perfect. Often, the service will suffer while parts are on order, or a software problem is being worked out. Even the best news servers will perform poorly for up to a week from time-to-time before things are fixed.