What is a host?
A host is a computer or other device that communicates with other hosts on a network. Also known as network hosts, hosts include clients and servers that send or receive data, services and applications.
Hosts typically do not include intermediary network devices like switches and routers, which are instead often categorized as nodes. A node is a broader term that includes anything connected to a network, while a host requires an IP address. In other words, all hosts are nodes, but network nodes are not hosts unless they require an IP address to function.
Hosts use various protocols to communicate, including TCP and User Datagram Protocol (UDP). On a TCP/IP network, each host has a host number that, together with a network identity, forms its unique IP address. In the Open Systems Interconnection (OSI) model, protocols in the transport layer, also known as Layer 4, are responsible for communication between hosts.
Types of IT hosts
The term host is used in several other areas within information technology (IT), carrying a slightly different meaning depending on the context.
For companies or individuals with a website, a host is a web server that stores and transmits the data for one or more websites. Host can also refer to the service provider that leases this infrastructure, which is known as hosting.
A cloud host is based on cloud computing technologies that enable a number of servers to act as one system in which website performance can be guaranteed by multiple machines. It often includes a network of servers pulling from different data centers in different locations.
Cloud hosts operate as a service that enables clients to buy as much of the service as they need. Cloud hosting is an alternative to hosting a website on a single server. Cloud hosting can be considered both infrastructure as a service (IaaS) and platform as a service (PaaS). Using a public cloud model, a public network transmits data that is physically stored on shared virtual servers that make up the cloud resource.
The term virtual host has two uses. One refers to the technology used to run multiple domains or applications on a single physical server. The second refers to companies that sell virtual infrastructure services.
In this context, users access a remote host in a different physical location using a private network or the internet. This process provides users with remote access. Examples include servers that users can log in to remotely or a host computer for a remote desktop.
Host virtual machine
This refers to the hardware -- or the physical server -- that provides the computing resources to support virtual machines (VMs). This process is also known as server virtualization.
Mainframe computer environments
In this context, a mainframe computer can be the host provider of services for the workstations attached to it. This does not mean that the host only has servers and the workstations only have clients. The server-client relationship is a programming model independent of this contextual usage of the term host.
A hostname is a plaintext name identifying a host in a given domain. On a local area network (LAN), a server's hostname might be a nickname like mailserver1. On the internet, a hostname makes up part of a web address and has three parts:
- domain name
- top-level domain
For example, an example hostname subdomain.example.com consists of the subdomain subdomain, the domain example and the top-level domain .com.
In other contexts, a host can also be a device or program that provides services to some smaller or less-capable device or program.
Editor's note: This definition was updated to improve the reader experience.