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 frequently referred to as a server. That machine might be a dedicated server or it used for other purposes. In the client/server programming model, a server program awaits and fulfils 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.
The term server can refer to a physical machine, a virtual machine or to the software that performing server services. The way that a server works varies considerably depending on how the word server is being used.
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 to drive down hardware costs since a single physical server can run multiple virtual servers, as opposed to each workload needing its own physical server.
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.
Servers are often categorized in terms of their purpose. A few examples of the types of servers available are as follows:
A web server is a computer program that serves requested HTML pages or files. In this case, a web browser acts as the client.
An application server is a program in a computer in a distributed network that provides the business logic for an application program.
A proxy server is software that acts as an intermediary between an endpoint device, such as a computer, and another server from which a user or client is requesting a service.
A mail server is an application that receives incoming emails from local users’ people within the same domain -- and remote senders and forwards outgoing emails for delivery.
A virtual server is a program running on a shared server that is configured in such a way that it seems to each user that they have complete control of a server.
A blade server is a server chassis housing multiple thin, modular electronic circuit boards, known as server blades. Each blade is a server in its own right, often dedicated to a single application.
A file server is a computer responsible for the central storage and management of data files so that other computers on the same network can access them.
A policy server is a security component of a policy-based network that provides authorization services and facilitates tracking and control of files.
A database server is responsible for hosting one or more databases. Client applications perform database queries that retrieve data from or write data to the database that is hosted on the server.
A print server provides users with access to one or more network-attached printers -- or print devices as some server vendors call them. The print server acts as a queue for the print jobs that users submit. Some print servers can prioritize the jobs in the print queue based on the job type or on who submitted the print job.
Saeed, L. (2020). What Is an Application Server? Introducing Jakarta EE CDI, 7-8. doi:10.1007/978-1-4842-5642-8_4
Techopedia.com. 2020. What Is A Server? - Definition From Techopedia. Available at: https://www.techopedia.com/definition/2282/server
BusinessDictionary.com. 2020. What Is A Server? Definition And Meaning. Available at: http://www.businessdictionary.com/definition/server.html