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.

A server is a computer or system that provides resources, data, services, or programs to other computers, known as clients, over a network. In theory, whenever computers share resources with client machines they are considered servers. There are many types of servers, including web servers, mail servers, and virtual servers.

An individual system can provide resources and use them from another system at the same time. This means that a device could be both a server and a client at the same time.

A server is a software or hardware device that accepts and responds to requests made over a network. The device that makes the request, and receives a response from the server, is called a client. On the Internet, the term "server" commonly refers to the computer system that receives requests for web files and sends those files to the client.

Initially, such servers were connected to clients known as terminals that did not do any actual computing. These terminals, referred to as dumb terminals, existed simply to accept input via a keyboard or card reader and to return the results of any computations to a display screen or printer. The actual computing was done on the server.

Later, servers were often single, powerful computers connected over a network to a set of less-powerful client computers. This network architecture is often referred to as the client-server model, in which both the client computer and the server possess computing power, but certain tasks are delegated to servers. In previous computing models, such as the mainframe-terminal model, the mainframe did act as a server even though it wasn’t referred to by that name.

While servers can run on different types of computers, it is important that the hardware is sufficient to support the demands of the server. For instance, a web server that runs lots of web scripts in real-time should have a fast processor and enough RAM to handle the "load" without slowing down. A file server should have one or more fast hard drives or SSDs that can read and write data quickly. Regardless of the type of server, a fast network connection is critical, since all data flows through that connection.

How a server works

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.

To function as a server, a device must be configured to listen to requests from clients on a network connection. This functionality can exist as part of the operating system as an installed application, role, or a combination of the two.

When a client requires data or functionality from a server, it sends a request over the network. The server receives this request and responds with the appropriate information. This is the request and response model of client-server networking, also known as the call and response model.

Server structures

The concept of servers is nearly as old as networking itself. After all, the point of a network is to allow one computer to talk to another computer and distribute either work or resources. Computing has evolved since then, resulting in several types of server structures and hardware.

Mainframe or minicomputer (AS/400)

You could say that the original servers, mainframe computers, and later, minicomputers, handled almost all computing tasks except the interaction with the user through a screen and keyboard, which was left to the client system

Computer hardware server

The next major wave of servers included computer-based servers. In many respects, these servers were nothing more than larger, more powerful desktop computers. Such servers were generally more expensive and held far more memory and disk space than most client computers. Each server was still a self-contained unit with its own motherboard, processor, memory, disk drives, and power supply. Servers like this were often warehoused in air-conditioned rooms called server rooms and were later bolted into racks for better storage and accessibility.

Blade servers

The original computer server hardware was large and stored in racks that could hold hundreds of pounds. Over time, however, faster means of connecting hardware resulted in parts of the server being extracted from a single self-contained device. By removing hard drives, eliminating internal cooling, and the ongoing miniaturization of computing parts, servers were eventually reduced to a single thin server known as a blade server. While still stored in racks in server rooms, blade servers are smaller and can be replaced more easily.

Combining servers

Even before virtualization, servers were being extracted from the standard model of a single server operating system installed on a hardware machine. Technology, such as network-attached storage, removed the need for a server to have its own storage. Other technologies, such as mirroring and clustering, enabled pieces of hardware to be combined into larger, more powerful servers. Such a server might consist of several blades, several attached storage devices, and an external power supply, and each piece could be swapped out for another while the server was still running.

Virtual servers

Virtual Servers still require hardware, but that hardware now runs a different process known as a hypervisor. In some cases, such as Microsoft’s Hyper-V, a full operating system continues to run on the hardware itself. In other cases, so-called bare-metal hypervisors can be installed directly onto server hardware. In both instances, the hardware itself is often spread across an array of blade servers, networked storage, and power supply, resulting in an environment where it is impossible to tell where any individual server ends and another begins.

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.

Examples of servers

The following list contains links to various server types.

How do other computers connect to a server?

With a local network, the server connects to a router or switch that all other computers on the network use. Once connected to the network, other computers can access that server and its features. For example, with a web server, a user could connect to the server to view a website, search, and communicate with other users on the network.

An Internet server works the same way as a local network server, but on a much larger scale. The server is assigned an IP address by InterNIC, or by a web host.

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