Servers: Client, Peer to Peer, Application Server, Database Server

Server is primarily a program that runs on a machine, providing a particular and specific service to other machines connected to the machine on which it is found. Generally speaking, a server is a machine with a specific set of programs that offer different types of service, which other machines (then called clients) request to do certain tasks. For example, a file server is a machine which keeps files, and allows clients to upload and download them from it. A web server is a machine that hosts web sites and allows Internet users (clients) to access these web sites.^[1] See also taxonomy of servers.

Here are some common types of servers:

A network server is a computer designed to process requests and deliver data to other (client) computers over a local network or the Internet. Network servers typically are configured with additional processing, memory and storage capacity to handle the load of servicing clients. Any computer can be a "network server". What separates a server from a workstation is not the hardware, but rather the function performed by the computer. In general, a workstation is any computer used by an individual person to perform his or her job duties, while a network server is any computer that provides users with access to shared software or hardware resources.

Client Server Networks

The term client-server model refers to a popular model for computer networking that utilizes client and server devices each designed for specific purposes. The client-server model can be used on the Internet as well as local area networks (LANs).
Examples of client-server systems

Client and Server Devices
Client devices are typically PCs with network software applications installed that request and receive information over the network. Mobile devices as well as desktop computers can both function as clients. A server device typically stores files and databases including more complex applications like Web sites. Server devices often feature higher-powered central processors, more memory, and larger disk drives than clients.

Client-Server Applications
The client-server model distinguishes between applications as well as devices. Network clients make requests to a server by sending messages, and servers respond to their clients by acting on each request and returning results. One server generally supports numerous clients, and multiple servers can be networked together in a pool to handle the increased processing load as the number of clients grows.
Some of the most popular applications on the Internet follow the client-server model including Web browsers, email, FTP clients, Web services, Web servers and DNS. Each of these clients features a user interface (either graphic- or text-based) and a client application that allows the user to connect to servers. In the case of email and FTP, users enter a computer name (or sometimes an IP address) into the interface to set up connections to the server.

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. ^[1]

Networking in JAVA

The Java networking is designed from the ground up to support concurrent programming, and java networking.

Peer-to-Peer ⇧

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.

Some articles:
• Client/server security issues • Client/Server Environment • Client-server versus peer-to-peer • Peer-to-peer networking • Security for Wireless Networks

Java networking:
• Given Above

Web Servers ⇧

A Web server is a program that, using the client/server model and the World Wide Web's HTTP, serves the files that form Web pages to Web users. Leading Web servers are Apache , the most widely-installed Web server, and Microsoft's Internet Information Server. Other Web servers include Novell's Web Server for users of its NetWare operating system and IBM's family of Lotus Domino servers, primarily for IBM's OS/390 and AS/400 customers. Web servers often come as part of a larger package of Internet- and intranet-related programs for serving e-mail, downloading requests for FTP files, and building and publishing Web pages. Considerations in choosing a Web server include how well it works with the operating system and other servers, its ability to handle server-side programming, security characteristics, and publishing, search engine, and site building tools that may come with it.^[2]

Apache

Apache is generally recognized as the world's most popular Web server (HTTP server). Originally designed for Unix servers, the Apache Web server has been ported to Windows and other network operating systems (NOS). The name "Apache" derives from the word "patchy" that the Apache developers used to describe early versions of their software.
The Apache Web server provides a full range of Web server features, including CGI, SSL, and virtual domains. Apache also supports plug-in modules for extensibility. Apache is reliable, free, and relatively easy to configure (About).

IIS

IIS is Microsoft's business-class Web server (About). Some corporations choose IIS as their Web server because it is supported by a commercial organization. Some have criticized IIS in the past, though, for its alleged security weaknesses. IIS has improved over the years, supports many Web standards including SSL, and integrates well with other Microsoft Web technologies such as FrontPage. Web developers can use Microsoft's Active Server Page (ASP)technology, which means that applications - including ActiveX controls - can be imbedded in Web pages that modify the content sent back to users. Developers can also write programs that filter requests and get the correct Web pages for different users by using Microsoft's Internet Server Application Program Interface (ISAPI) interface. An admininstrator can manage IIS through a graphical console, the Internet Services Manager.

Comparison and security of web servers:
IIS vs. Apache, Security Tips for Server Configuration, General Server Security, Server Security Policy , Web and Database Server Security