Remote Procedural Call (RPC) is a protocol used by computer programs that allow them to request services from other programs running on other computers on a network. A Remote Procedural Call Server (RPC Server) is a program that listens for incoming RPC requests and provides the requested services.

In the RPC model, a client program sends a request message to a server program, which performs the requested service and sends a response message back to the client. This mechanism allows programmers to write distributed applications that can run on different machines and operating systems.

An RPC Server operates by exposing a set of procedures or functions that can be called remotely by client programs. Before calling a procedure, the client establishes a connection with the server, using a network protocol such as TCP/IP or HTTP. The client then sends a request message to the server that includes the name of the procedure to be called and any input parameters. The server processes the request, performs the procedure, and sends back a response message to the client, including any output parameters or return values.

RPC Servers offer several advantages over other distributed computing models. They provide a simple, standardized interface that allows different programs to communicate with each other, regardless of the underlying technology used. Additionally, because the server manages the resources needed to perform the requested service, the client program can be simpler and easier to develop.

RPC Servers are commonly used in enterprise applications, where multiple systems or services need to communicate with each other. They can be found in operating systems, middleware, databases, and web services. Examples of RPC protocols include Microsoft’s Remote Procedure Call (RPC), Sun’s Remote Method Invocation (RMI), and XML-RPC.

The implementation of RPC Servers can be complex, requiring careful consideration of issues such as security, scalability, and fault tolerance. However, once implemented correctly, they offer a powerful and flexible mechanism for building distributed applications.