A newsgroup server is the heart and soul of every Usenet system. When someone speaks of their retention, connection speeds, or any other service metric, they are giving a measure of the ability of their newsgroup server.
It's not always necessarily correct to use the singular term 'server', as many Usenet systems operate many servers that work in tandem. This is referred to as a 'server cluster' or 'server farm'. There are a number of advantages to this structure, one of the most important being redundancy. In the case of PowerUsenet, this means that if one server in our cluster runs into performance issues, the others can pick up the slack, and users of the service would notice no hiccups or decline in quality.
News server retention is directly related to the hard drive space available on a newsgroup server. More hard drive space allows a news server to retain a larger volume of articles. A large amount of hard drive space is a particular necessity for hosting binary articles, because a single posting can be many gigabytes in size. A single newsgroup server with a small hard drive might be able to retain articles for a few hours, where an entire cluster of newsgroup servers might be able to retain articles for over a month.
Connection speed is also relatable to a newsgroup server, but it is not primarily limited by the server's hardware. Newsgroup server operators pay a service provider for an internet connection, just like residential users. This connection is quite a bit faster (and more expensive!) than those provided to residential users, and the bandwidth of the connection is guaranteed in a contract. Even though the pipeline carries this guarantee, server hardware can also affect the speed users see. For example, if an extremely large amount of users are connected to a server, its processor and memory might not be able to efficiently handle every user, and the overall speed could decline. Essentially, the server can become too overwhelmed to efficiently and thoroughly provide reliable speed.
The server itself is the single most important piece of equipment to a newsgroup system. Nearly every measurable performance statistic depends on the capabilities of the newsgroup server. At PowerUsenet, our newsgroup servers are capable of handling even the most demanding users. Our newsgroup servers have the storage to guarantee 40 days of binary article retention in every newsgroup, and we frequently upgrade this capacity to keep up with increased posting volume. Our server clusters are peered with some of the largest ISP and backbone internet providers in the world, which allows us to guarantee the fastest speeds possible. We also employ a clustering strategy that guarantees that even at peak usage times, our servers won't begin to even break a sweat.
For end-users, the importance of the server is obvious — consistent, reliable performance is what separates a truly 'premium' provider from basement operations.