Server

Server

 A server is a computer program or device that provides a service to another computer program and its user, also known as the client. In a data center, the physical computer that a server program runs on is also frequently referred to as a server. That machine might be a dedicated server or it might be used for other purposes.

In the client/server programming model, a server program awaits and fulfills requests from client programs, which might be running in the same, or other computers. A given application in a computer might function as a client with requests for services from other programs and as a server of requests from other programs.

How servers work

The term server can refer to a physical machine, a virtual machine or to software that is performing server services. The way that a server works varies considerably depending on how the word server is being used.

Physical and virtual servers

A physical server is simply a computer that is used to run server software. The differences between a server and a desktop computer will be discussed in detail in the next section.

A virtual server is a virtual representation of a physical server. Like a physical server, a virtual server includes its own operating system and applications. These are kept separate from any other virtual servers that might be running on the physical server.

The process of creating virtual machines involves installing a lightweight software component called a hypervisor onto a physical server. The hypervisor's job is to enable the physical server to function as a virtualization host. The virtualization host makes the physical server's hardware resources -- such as CPU time, memory, storage and network bandwidth -- available to one or more virtual machines.

An administrative console gives administrators the ability to allocate specific hardware resources to each virtual server. This helps dramatically drive down hardware costs because a single physical server can run multiple virtual servers, as opposed to each workload needing its own physical server.

Server software

At a minimum, a server requires two software components: an operating system and an application. The operating system acts as a platform for running the server application. It provides access to the underlying hardware resources and provides the dependency services that the application depends on.

The operating system also provides the means for clients to communicate with the server application. The server's IP address and fully qualified domain name, for example, are assigned at the operating system level.