VMware vSphere is a suite of software components for virtualization. These include ESXi, vCenter Server, and other software components that fulfill a number of different functions in the vSphere environment.

vSphere includes the following software components:


A virtualization platform that you use to create the virtual machines as a set of configuration and disk files that together perform all the functions of a physical machine.

Through ESXi, you run the virtual machines, install operating systems, run applications, and configure the virtual machines. Configuration includes identifying the virtual machine’s resources, such as storage devices.

The server provides bootstrapping, management, and other services that manage your virtual machines.

vCenter Server

A service that acts as a central administrator for VMware ESXi hosts that are connected on a network. vCenter Server directs actions on the virtual machines and the virtual machine hosts (the ESXi hosts).

vCenter Server is a single Windows Service and is installed to run automatically. vCenter Server runs continuously in the background. It performs its monitoring and managing activities even when no vSphere Web Clients are connected and when no one is logged on to the computer where it resides. It must have network access to all the hosts it manages and be available for network access from any machine where the vSphere Web Client is run.

You can install vCenter Server in a Windows virtual machine on an ESXi host, allowing it to take advantage of the high-availability that is provided by VMware HA. See the vSphere Installation and Setup documentation for details about setting up this configuration.

You can join multiple vCenter Server systems using Linked Mode to allow them to be managed using a single vSphere Web Clientconnection.

vCenter Single Sign On

A service that is part of the vCenter Server management infrastructure. The vCenter Single Sign On authentication service makes the VMware cloud infrastructure platform more secure by allowing the various vSphere software components to communicate with each other through a secure token exchange mechanism, instead of requiring each component to authenticate a user separately with a directory service like Active Directory.

When you install vCenter Single Sign-On, the following components are deployed.

STS (Security Token Service)

STS certificates enable a user who has logged on through vCenter Single Sign-On to use any vCenter service that vCenter Single Sign-On supports without authenticating to each one. The STS service issues Security Assertion Markup Language (SAML) tokens. These security tokens represent the identity of a user in one of the identity source types supported by vCenter Single Sign-On.

Administration server

The administration server allows users with administrator privileges to vCenter Single Sign-On to configure the vCenter Single Sign-On server and manage users and groups from the vSphere Web Client. Initially, only the user administrator@vsphere.local has these privileges.

vCenter Lookup Service

vCenter Lookup Service contains topology information about the vSphere infrastructure, enabling vSphere components to connect to each other securely. Unless you are using Simple Install, you are prompted for the Lookup Service URL when you install other vSphere components. For example, the Inventory Service and the vCenter Server installers ask for the Lookup Service URL and then contact the Lookup Service to find vCenter Single Sign-On. After installation, the Inventory Service and vCenter Server system are registered in vCenter Lookup Service so other vSphere components, like the vSphere Web Client, can find them.

VMware Directory Service

Directory service associated with the vsphere.local domain. This service is a multi-tenanted, multi-mastered directory service that makes an LDAP directory available on port 11711. In multisite mode, an update of VMware Directory Service content in one VMware Directory Service instance results in the automatic update of the VMware Directory Service instances associated with all other vCenter Single Sign-On nodes.

vCenter Server plug-ins

Applications that provide additional features and functionality to vCenter Server. Typically, plug-ins consist of a server component and a client component. After the plug-in server is installed, it is registered with vCenter Server and the plug-in client is available to the vSphere Web Client for download. After a plug-in is installed on the vSphere Web Client, it might alter the interface by adding views, tabs, toolbar buttons, or menu options related to the added functionality.

Plug-ins leverage core vCenter Server capabilities, such as authentication and permission management, but can have their own types of events, tasks, metadata, and privileges.

Some vCenter Server features are implemented as plug-ins, and can be managed using the vSphere Web Client Plug-in Manager. These features include vCenter Storage Monitoring, vCenter Hardware Status, and vCenter Service Status.

vCenter Server database

A persistent storage area for maintaining the status of each virtual machine, host, and user managed in the vCenter Server environment. The vCenter Server database can be remote or local to the vCenter Server system.

The database is installed and configured during vCenter Server installation.

If you are accessing your ESXi host directly through the vSphere Web Client, and not through a vCenter Server system and associated vSphere Web Client, you do not use a vCenter Server database.


Many vCenter Server functions are implemented as Web services that require the tcServer. The tcServer is installed on the vCenter Server machine as part of the vCenter Server installation.

Features that require the tcServer to be running include: Linked Mode, CIM/Hardware Status tab, Performance charts, WebAccess, vCenter Storage Monitoring/Storage Views tab, Storage Policy-Based services, and vCenter Service status.

vCenter Server agent

On each managed host, the software that collects, communicates, and executes the actions received from vCenter Server. The vCenter Server agent is installed the first time any host is added to the vCenter Server inventory.

Host agent

On each managed host, the software that collects, communicates, and executes the actions received through the vSphere Web Client. It is installed as part of the ESXi installation.


vCenter Server uses LDAP (Lightweight Directory Access Protocol) to synchronize data such as license and role information across vCenter Server systems joined in Linked Mode.