They are implemented as custom Microsoft Windows programs that talk to a centralized server and database.

The architecture of P2P systems vary - some rely upon a centralized server, others are decentralized with no one site operating the system.

For example, as all contents are stored in centralized servers, it does not require a comprehensive content distribution system.

It also borrows from the corporate world by relying on data stored on a centralized server to make everything happen.

Castle would have made it possible to have an identification service, which provides user authentication, for all members on the network, without a centralized server.

The idea was Software as a Service, or cloud computing, using software running on a centralized server.

The software runs on a centralized server, allowing multiple clients to connect simultaneously.

Soribada 2.0 allowed users to swap files without having to cross through a centralized server.

An imagined system for serving these descriptions from a centralized server is described in the Phetch paper.

Having a centralized server limits the ability to work in disconnected manner.