Messages are sorted according to a subject which is named a newsgroup . It's usual for news servers to have a list of some thousands groups. We're interested in groups with messages containing any attached files. There is about a thousand of groups containing binary attachments in the messages on a big provider's news server. It's a huge volume of constantly changing information.
Every news server contains some news groups containing some messages.
News servers exchange new messages. The lists of groups are usually the same for different news servers, but not completely. The speed of your computer connection to your internet-provider is your maximum speed of Internet connection. That's why you have the highest speed downloading anything from you provider's server. In common, internet-providers have their own news servers available for their clients.