Client-Server vs Peer-to-Peer and Other Models

The client-server model was originally developed to allow more users to share access to database applications. Compared to the mainframe approach, client-server offers improved scalability because connections can be made as needed rather than being fixed. The client-server model also supports modular applications that can make the job of creating software easier. In so-called "two-tier" and "three-tier" types of client-server systems, software applications are separated into modular pieces, and each piece is installed on clients or servers specialized for that subsystem.
Client-server is just one approach to managing network applications The primary alternative, peer-to-peer networking, models all devices as having equivalent capability rather than specialized client or server roles. Compared to client-server, peer to peer networks offer some advantages such as more flexibility in growing the system to handle large number of clients. Client-server networks generally offer advantages in keeping data secure.