XenDesktop is software made by Citrix Systems which provides users remote access to another computer’s desktop (remote computer). This remote computer has an operating system such as Microsoft Windows 7, along with a configured set of applications and is ready for use for the connecting user. The user has sole access to the remote computer and unlike XenApp where the remote desktop is shared.
The remote computer is commonly a physical computer or a software emulated computer (virtual computer) running on another physical computer (host) using virtualization software known as a Hypervisor.
The current version is XenDesktop 7.8, release in February 2015.
The term Virtual Desktop Infrastructure (VDI) is used to describe systems such as XenDesktop. Where multiple virtual computers running a desktop operating system such as Windows 7, are created on a Hypervisor by a provisioning service.
The term ‘Hypervisor’ is used to describe the function of emulating computers (hosting) using virtualization software such as XenServer, VMWare vSphere or Microsoft Hyper-V.
The hypervisor software is installed on a physical computer and provides the ability to share resources from the physical computer with the multiple virtual computers created by the Hypervisor software.
XenDesktop controls and manages the process to create virtual machines on the Hypervisor. This process is called provisioning, where virtual desktops (virtual machines running a desktop operating system like Microsoft Windows 7) are created from a master image.
The controller marshals user connections, ensuring they reach the appropriate virtual desktop on the hypervisor. The controller also monitors the connection between the users and the virtual desktops assigned to them.
The controller controls the ability to select a dedicated virtual desktop (assigned solely to a user) or from a pool of virtual desktops (user is randomly connected to the next available virtual desktop in the pool).
XenDesktop allows a single image of the desktop operating system, such as Windows 7, to be created and multiple copies of this image to be made quickly. The users then access one of the copies of the master image. This master image is a reference image, which is configured for the users to use and has the applications added to it.
The XenDesktop system requires:
– StoreFront (previously Web Interface) (a web based access) to provide the interface for authentication and authorization of users to the system,
– Database to store information on a database server,
– Controller(s) which direct users to their assigned desktops,
– Hypervisor to host the virtual machines (virtual desktops) and a,
– Provisioning service either Provisioning Server or Machine Creation Services (MCS).
XenDesktop vs XenApp
While XenDesktop allows users sole access to remote virtual computers. XenApp software, instead allows several users to interact with a single remote computer at the same time
XenApp does this by displaying a separate image (of applications or desktops) to each user and by isolating their interactions from each other.
Unlike XenApp where users will see individual applications presented to them (unless the desktop is published). XenDesktop users, will be presented with a full screen showing the remote computer’s desktop. This makes it appear as though the user is using the computer directly.
As the users share resources on the remote computer with XenApp, this creates contention (many users may slow down the user interaction) while XenDesktop is less likely to do so as the user has sole access to the remote computer. By having too many virtual machines running on the Hypervisor may cause contention in XenDesktop access.
XenDesktop is available in three editions, the entry level XenDesktop VDI Edition, the mid level XenDesktop Enteprise Edition and the premium level XenDesktop Platinum Edition.
XenDesktop VDI Edition
The base version provides the ability to deliver VDI computers (remote virtual computers) which can include personal vDisks. The vDisks allow any changes made by users such as customisation of their desktops to be saved. This is important as the remote virtual computer used delivered by XenDesktop may not have the ability to save changes such as a pooled desktop.
XenDesktop Enterprise Edition
This is the enterprise level and includes additional features on top of the Advanced Edition.
XenDesktop Platinum Edition
This is the premium version of XenDesktop.
XenDesktop can use either a concurrent licensing model or a named user or a named device licensing model.
The concurrent license model considers the total number of users using XenDesktop at the same time. So a company may have 1,000 people who need to use XenDesktop but only 200 will be using it at any one time. Therefore 200 users would be classed as concurrent.
The named user or named device licensing model either licenses the total number of users who will be using XenDesktop or the total number of computers (devices) which will use XenDesktop provided virtual desktops.
The named user or device license model does not consider concurrent users, so if a 1,000 users are going to connect, then a 1,000 of these licenses will be required, even if only a maximum of 200 users are connected at any one time.