Released in April 2007, Citrix Desktop Server 1.0 (CDS) was previously code-named Project Trinity. Citrix Desktop Server was the first purpose-built solution with the DynamicDelivery technology, which automatically selected the right type of virtual desktop, and thus enabling IT administrators to deliver the best desktop for each user according to their needs. It supported all three of the most popular ways of installing a desktop operating environment in a data centre. It included Windows Terminal Server (TS), the server-hosted virtual desktop infrastructure (VDI), and blade PCs-based assigned workstation desktops (blades). It featured two desktop delivery models:

Workstation desktops can be pooled or assigned. The 32-bit Windows XP OS was supported for desktops. The product was priced starting at $75 per named user.

Released in May 2008, after the acquisition of Ardence and XenSource, Citrix announced the release of XenDesktop 2.0. Citrix combined the desktop virtualization capabilities of XenEnterprise v4 with its Citrix Desktop Server product line, thereby forming a new product called XenDesktop. XenDesktop 2.0 used to be shipped in five editions.

It featured the Active Directory authentication, Desktop Delivery Controller, XenApp for Virtual Desktops, Provisioning Server, Desktop Receiver for Windows XP, and Windows Vista. It also supported the 32-bit Windows XP SP2 and the Windows Vista desktop operating systems. It supported hypervisor versions, such as Citrix XenServer 4.1, SCVMM 1.0, and VMware Infrastructure 3 (VMware ESX). The pricing model has been changed to concurrent user's mode, which begins at $75 per concurrent user.

Released in September 2008, XenDesktop 2.1, in addition to enhanced components, it featured a Software Development Kit (SDK) and a way of creating disabled desktop groups. It supported the 64-bit version of Windows XP SP2 and the Windows Vista desktop operating systems. The hypervisor support was extended to the Windows Server 2008 Hyper-V and the respective SCVMM version.

Released in February 2009, XenDesktop 3.0 introduced the HDX technologies, including HDX MediaStream, HDX Plug-and-Play, and HDX Broadcast. At that time, the other new features were smart card support, profile management, local peripheral support, and user-driven desktop restart. It supported Windows XP SP3 and the Windows Vista 32-bit desktop operating systems. The hypervisor support remained the same. The pricing began at $75 per concurrent user.

Released in November 2009, XenDesktop 4.0 introduced the FlexCast technology for improving scalability across multiple virtual desktop delivery models and for enabling enterprises to deliver virtual desktops to more users at a far lower cost. XenDesktop 4 includes all the functionalities of XenApp as an integrated feature, and it makes delivering on-demand applications a seamless part of the overall desktop management strategy.

The new features, such as active directory multi-forest support, site roaming and site failover for disaster recovery, IPv6 support, password manager, branch repeater integration, and alternate protocols /RDP integration have been included in this version. Enhancements have also been made to EdgeSight and profile management components. The HDX enhancements, such as plug-n-play USB Support, plug-n-play multi-monitor support, IntelliCache, and HDX 3D Pro graphics have been included in this version. The desktop support is extended to operating systems, such as Windows 7 (non-Aero) 32-bit or 64-bit, and 64-bit Windows XP and Windows Vista. The hypervisors support included Citrix XenServer 5.5, VMware Infrastructure 3, and VMware vSphere 4/4.1, and SCVMM 2008 & SCVMM 2008 R2.

Citrix changed the licensing to the named user pricing model. The XenDesktop 4 pricing began at $75 per named user for the standard edition. The VDI edition was priced at $95 per named user or $195 per concurrent user. The enterprise and the platinum editions were tagged at $225 and $350 per named user respectively. Citrix also started trade-up to XenDesktop 4 program, through which XenApp customers can trade their existing XenApp concurrent user licenses for a better version of XenDesktop. For one XenApp license, the customers would receive two XenDesktop 4 user licenses. Moreover, the trade-up starts at $45 per user.

Released in December 2010, XenDesktop has been re-written and re-architected, bringing unprecedented levels of simplicity for both the users and IT professionals and developers. XenDesktop moved away from Independent Management Architecture (IMA) to a new architecture called FMA, which has been written almost completely in .NET. A remote desktop service (formally Terminal Services) is no longer required on Desktop Delivery Controllers (DDC) and it doesn't use the IMA data store.

For end users, an entirely redesigned virtual desktop viewer makes the workspace feel familiar and inviting. The powerful new HDX enhancements include the support for 32-bit color, dynamic color compression, HDX RealTime video conferencing, and large-file printing optimizations. These would dramatically improve the performance of the system even over low bandwidth connections. It has improved the smart card single sign-on from the non-domain-joined user devices. It also supports an entirely new generation of web and software-as-a-service (SaaS) apps. Citrix unveiled an extensive new initiative to help customers move from the wow of desktop virtualization to the how of successful implementation.

For IT, its role-based features have greatly simplified the management tasks and reduced the total number of management consoles. The new Desktop Studio console has been designed for administrators, and the new Desktop Director console has been designed for Helpdesk users. The new installer makes it faster and more powerful, so much so that you can complete a new installation in 10 minutes. It introduced a new technology for easily creating virtual desktops, called Machine Creation Services (MCS), and single image desktop management. Microsoft remote assistance is now used for shadowing user desktop sessions. It has simplified policy administration by integrating Active Directory group policies. It has extended the FlexCast technology for supporting the new XenClient hypervisor and it has also extended the hypervisor support to XenServer 6, VMware vSphere 5.0, and SCVMM & Hyper-V for Windows Server 8 and SCVMM 2012. In addition, it introduced a comprehensive new SDK, which enables customers and partners to integrate and automate solutions with third-party systems management tools. The virtual desktop supported 64-bit Windows XP, Vista SP2, and Windows 7 (non-Aero).

The pricing for the VDI-only edition starts at $95 per user or device. The whole desktop and application virtualization in Enterprise and Platinum editions cost $225 and $350 respectively.

Released in August 2011, it introduced the Personal vDisk technology, acquired from RingCube, which made the virtual desktops personal. XenDesktop 5.5 witnessed 150 new features, and these are the most significant enhancements ever to have been made to HDX technology, resulting in three times faster (HDX Broadcast) delivery of virtual desktops over the WAN to mobile and branch office workers. Printing and scanning became six times faster, and app launching became two times faster. There have been new Quality of Service (QoS) controls for ensuring superior user experience across any network conditions. It included significant multimedia, voice and video enhancements. It also comes with a new flash redirection technology, which delivers stunning video and audio experience even over WAN.

The HDX components included the following:

It supports faster application delivery with the inclusion of the new Citrix XenApp 6.5 as an integrated feature. The new instant app access feature reduced the application launch times by almost 50 percent. It unveiled unparalleled native user experience on smart phones and tablets. It has enhanced the support for Microsoft technologies, including Microsoft RemoteFX, which provides Aero-based Windows 7 desktops, and App-V management tools integration. Hypervisor support has remained almost the same. The virtual desktop support was extended to Windows 7 Aero 32-bit or 64-bit.

Released in March 2012, this new version has fully integrated personalization technology with the addition of two new types of catalogues. The new catalogue are "pooled with the help of personal vDisk" (for pooled-static virtual desktops), which you can manage with the help of Desktop Studio, and "streamed with personal vDisk", which you can manage with the help of provisioning services. It has fully integrated the support for Microsoft System Center 2012 Configuration Manager (SCCM 2012) and for Microsoft System Center 2012 Virtual Machine Manager (SCVMM 2012). Citrix also announced the release of Citrix AppDNA 6 software, which enables the rapid assessment and migration of applications.

The virtual machines with personal vDisks are supported by Windows XP 32-bit with SP3 and Windows 7 (non-Aero). The supported virtual machines without personal vDisks include Windows XP, Windows Vista (non-Aero) with SP2, and Windows 7 (non-Aero).

Released in June 2013, XenDesktop 7 is the first product release of the Project Avalon. It is called the Excalibur release. Project Avalon is a multi-phased initiative by Citrix for delivering Windows apps and desktops as Cloud services. XenDesktop 7 integrates both XenApp and XenDesktop technologies into a new unified and Cloud-style FMA. It has enabled scalable, simple, efficient, and manageable solutions for delivering Windows applications and desktops.

Citrix released new and redesigned management and delivery components, which provide administrators with a unified management experience. It has made XenDesktop 7 available in app edition. It has devised a new, streamlined installer, which will guide you through the installation of all of core components, such as delivery controller, StoreFront, license server, studio, director, and Virtual Delivery Agents (VDAs).With EdgeSight integration, the web-based director user interface has been redesigned. StoreFront replaced the Web Interface component and featured enhancements including desktop appliance sites. MCS supported the creation of desktops and server OS VMs. For XenApp administrators, the entire XenDesktop FMA architecture brings a lot of new concepts, features, component mappings, and learnings.

XenDesktop 7 featured new HDX mobile technologies, which deliver an intuitive and mobile-friendly experience. The fully incorporated H.264 compression raised the WAN bandwidth efficiency, added innovative touch screen capabilities, and provided support for translating multi-touch gestures and finger swipes into smooth navigation and scrolling commands. New compression capabilities for supporting the dynamic optimization of the full HD video (webcam) bit rate has made HD videos viewable on 3G mobile networks. It included Windows Server 2012 and Windows 8 support, desktop composition redirection, Windows media client-side content fetching, multicast support, real-time multimedia transcoding, User Datagram Protocol (UDP) audio for server OS machines, HDX 3D Pro, rich graphics and video rendering from the server side, and improved flash redirection.

XenDesktop 7 is built as an open platform, and it supports deployment on any hypervisor or Cloud management solution, including the Citrix Cloud platform (which is powered either by Apache CloudStack) or Amazon Web Services (AWS). It introduced the addition of new capabilities, such as the following:

The Citrix Ready partners deliver XenDesktop 7 optimized solutions, such as:

The Host hypervisor support included:

The virtual desktops support the following:

The minimum supported provisioning services version is 7.0, and the License Server is v11.11.

Citrix has discontinued most of the legacy features in this release, including:

The XenDesktop 7 editions were available in licensing modes, such as per-user, per-device, or on a concurrent basis. The new XenDesktop app edition was made available only for XenApp customers who were using the entire hosted-shared (RDS) app and published desktop workloads. The upgrade to the XenDesktop app edition was offered without any additional charge for XenApp Enterprise and Platinum customers with an active subscription.

Released in October 2013, Citrix termed XenDesktop 7.1 as a platform. The XenDesktop platform is based on the new architecture Simplified FlexCast Management, which is compatible with the latest Microsoft technologies. The new features include the Virtual Graphical Processing Unit (vGPU), which allows multiple VMs to access a single physical GPU, and provides full support to 3D graphics. The Graphical Processing Unit (GPU) capabilities redirect flash- graphics for OS, such as Windows 8.1, Windows 8, Windows Server 2012, and 2012 R2. It supports virtual desktops and applications for the operating system Windows 8.1 and Windows Server 2012 R2.

It supports the following hypervisor solutions:

In March 2014, along with XenDesktop 7.5, Citrix released XenApp 7.5 as a separate product, which shared the unified FMA architecture and management. XenDesktop takes the enterprise desktop virtualization deployments to hybrid provisioning by allowing businesses to use public Clouds, such as AWS or any Citrix Cloud Platform that is powered by the Apache CloudStack Cloud. This improves their flexibility and leads to the growth or transformation of their virtual desktop infrastructure. While the hypervisor's support is extended to VMware vSphere 5.5, neither VMware vSphere 5.5 nor Hyper-V hypervisors are supported by the Citrix CloudPlatform. The Citrix CloudPlatform only supports XenServer 6.2. On the other hand, AWS doesn't offer the desktop operating system instances. So, you can provision the applications and desktops only on supported Windows server operating systems.

The remote PC access is enhanced such that it supports the Wake on the LAN for PCs that support Intel Active Management Technology (AMT), or PCs with the Wake on the LAN option enabled in the BIOS. Also included full AppDNA support for the automated analysis of Windows application suitability for application virtualization through XenApp, App-V, or XenDesktop. It also features StoreFront 2.5 and supports Web Interface 5.4 without providing support for any additional operating systems or enhancements. The virtual desktops operating system support remains the same.

Citrix announced two new Citrix Ready programs for driving the hybrid Cloud and low-cost initiatives. The new Citrix Ready Infrastructure-as-a-Service (IaaS) Cloud for XenDesktop supports businesses by helping them find a Cloud operator whose infrastructure supports XenDesktop. Citrix Ready low-cost converged infrastructure verified solutions are tested for their scalability deployments, which range from a few hundred to a few thousand desktops. These provide performance and maintain a high availability of resources. Citrix also introduced a limited time XenMobile promotion, which included a free XenMobile MDM or 20 percent off the XenMobile enterprise for XenApp and XenDesktop platinum edition customers, which was valid until September 30, 2014.

Released in September 2014, XenDesktop is built on third-generation FMA, and it is designed to be deployed in the Cloud and in hybrid environments. It features instant access to virtual apps by retaining the application pre-launch, session linger, and anonymous logon features that were made popular by the earlier versions of XenApp. The new connection leasing feature enables high availability and provides resilience in withstanding the temporary loss of database. It delivers an unmatched user experience through improved graphics performance, which includes improved image sharpening, visually enhancing the lossless compression, and extending the DirectX/2D rendering capabilities. It is also USB 3.0 ready, and it provides the generic redirection of the latest USB 3.0 peripherals, such as webcams, headsets, and Lync phones. To enhance the user experience of Windows apps on the mobile devices, Citrix released a new update for the HDX Mobile SDK. The new enhancements in provisioning services employ commodity servers and the RAM so that the IOPS load on storage is dropped by 99 percent, which obliterates the cost barriers for delivering high-performance storage.

It's the only unified platform which is Federal Information Processing Standards (FIPS) compliant under the Common Criteria (CC) evaluation. It features the security enhancements that enable the granular policies over clipboard content filtering and directional control, so that potentially malicious data, perhaps embedded in the Rich Text Format, cannot be pasted to the secured environment. It supports the secure connections between users and VDAs. The Platinum edition includes the full power of the Citrix AppDNA application migration technology, which simplifies app migrations to the latest versions of Windows. In close partnership with Microsoft, Citrix developed the Citrix Connector 7.5 for System Center Configuration Manager (SCCM), and it has released a new reference architecture for deploying XenApp and XenDesktop on Microsoft Azure, which materializes the Citrix Workspace Services vision on Azure. It integrates and enhances the existing XenApp 6.5 deployments, and it also streamlines the Cloud deployments with the verified IaaS providers.

Enhancements have been made to Citrix Studio and Citrix Director. The new features in Studio include enhanced reporting and application folders. The new features in Director include licensing alerts, the view hosted applications usage, monitoring hotfixes, an expanded filtering feature, and the Director has also been made compatible to XenApp 6.5. The enhanced connection throttling settings provide control and they improve host performance.

They support both the virtual IP and the virtual loopback for the applications published on machines running Windows Server 2008 R2 and Windows Server 2012 R2. The Remote PC access enhancement limits a local user from disconnecting a remote session without the permission of a remote session user. It provides support for the HDX Real-Time Optimization Pack 1.5 for Microsoft Lync. It also provides support to the receiver for Chrome 1.4 and the Receiver for HTML5 1.4. These receivers include the ability to convert document files into PDF files from hosted applications or applications running on the virtual desktops, so that users can view and print them from their local device.

The new Citrix StoreFront 2.6 has the following features:

The virtualization resource support has been extended to XenServer 6.2 SP1 with hotfixes. The virtual desktops operating system support remains the same. The Citrix CloudPlatform supports XenServer 6.2 SP1 with hotfixes, VMware vSphere 5.5, and it does not support the Hyper-V hypervisors.

Citrix XenDesktop uses the Citrix Receiver, which is a universal client built with a vision of supporting any device and any platform. It currently supports all mobile and desktop device platforms, including Windows, Mac, Linux, iOS, Android, ChromeOS, and Blackberry. It also supports Thin Client environments, which require a zero-install option and a clientless HTML5 Receiver, which is available for web-based access. It works natively on a broad range of physical devices, including desktops, laptops, tablets, and smart phones. Citrix Receiver has been made available on many popular online application stores, which has made it simpler to install and use on BYOD or corporate devices. It has been designed to easily adopt the features of the native device, including scrolling the native menus, multi-touch, and pop-up controls, GPS, and cameras, specifically on touch based mobile devices.

XenDesktop users can access their desktops, corporate applications, web, SaaS, and their secure ShareFile integrated user data on any device, at anytime and from anywhere. This enables complete workplace flexibility, business continuity, and user mobility.

Citrix High Definition (HDX) user experience technologies have been built on top of the Citrix ICA protocol, which is renowned for the best-of-breed networking. It represents 25 years of innovation and excellence. The ICA protocol in itself is based on the basic TCP/IP and RTP/UDP protocols, and it has been uniquely designed for traversing the difficult network topologies that range from variable mobile networks to high latency low-bandwidth WANs. HDX is a unique strength of XenDesktop, and it makes the virtual desktop delivery experience extremely responsive and fast.

The Citrix ICA protocol was primarily used for streaming application and terminal session screen updates by XenApp. Citrix ported this ICA protocol for delivering a Windows desktop operating system, and they had initially named it PortICA. The underlying architecture of PortICA remained the same. It uses the virtual channels. PortICA was turned into the HDX technology in the later releases. HDX has been a part of Project Avalon Excalibur, and it has been enhanced by enormous capabilities.

The Citrix HDX technologies are the foundation of the Citrix application (XenApp) and desktop delivery (XenDesktop) platforms. They provide superior high-definition user experience on any device, over any network. It delivers an unparalleled experience, even while using real time audio and video collaboration, rich multimedia, the latest USB peripherals and 3D graphics. As Windows apps became optimized for mobile devices, they improved their support for touch gestures and other native device features. The integrated WAN optimization capabilities of HDX deliver a satisfying user experience, even over challenging low-bandwidth and high-latency networks. When using XenDesktop and the HDX technologies, IT departments can successfully extend the delivery of the virtual desktops beyond the corporate headquarter offices to remote, mobile, and branch office users.

Knowing the HDX internals involves understanding the three technical principles that it is made of. These are:

At run time, these work towards delivering an optimized user experience, reduced bandwidth consumption, and improved scalability of the rendering server.

Intelligent redirection

This involves examining user screen activity, application commands, and the user endpoint device, which connects the network and hosting server capabilities, so that they can dynamically determine how and where to render an application or a desktop activity. The redirection operation can occur on either the local client or the central VDA. Redirection at the client offloads all the processing from the server and places it on the client's device. The device and the peripheral redirection lets the peripherals, such as webcams, printers and scanners, to be terminated locally, so that users can interact with these devices at native USB speeds.

The following figure is a diagrammatic illustration of the steps that were used in the intelligent redirection process. It also indicates the various virtual channels, the network layers, and the protocols that were involved in the HDX technology.

As in the case of traditional physical desktops, it is not possible to meet every user's requirements with a single desktop type because different types of business users need different types of desktop setups. This has been the greatest limitation for businesses when it comes to adopting desktop virtualization technologies. In a business organization, some users will require simplicity and standardization, while other users will require a highly personalized and more performance equipped system. If a single desktop virtualization model is implemented across an entire organization, it will inevitably lead to reduced user productivity.

FlexCast is a delivery technology which enables IT to deliver every type of virtual desktop, such as hosted, local, physical, or virtual- each specifically tailored to meet the performance, security, personalization, mobility and flexibility requirements of each user. This approach is unique and it is dramatically different from the way in which most other vendors look at desktop virtualization. Six FlexCast models are available, and each one provides different capabilities, based on the unique user group requirements.

It is very important to assess the business user requirements, and then choose the right FlexCast model for using resources efficiently and for providing the best end user experience.

On-demand apps

The on-demand apps FlexCast model centralizes the Windows applications in the data centre, and enables instant accessing through high-speed protocol (requires connection), or it can also be streamed (offline support) through Microsoft App-V. It does not provide users with virtual desktops, but provides them with Windows applications.

The following figure is a very informative comparison table, which covers the various FlexCast model supports that have been provided by XenDesktop version 7.x. Using this table, you can easily opt for a FlexCast model for a given user case requirement.

In today's businesses, IT prioritizes the centralization and simplification of desktop infrastructure for reducing the total cost of ownership. This leads to the move of desktop infrastructure to a Cloud that enables maximum benefits and capabilities for businesses. However, at present, businesses have made huge investments in various hypervisors, storage, and Microsoft infrastructures. Most of the businesses need a hybrid solution, which would leverage the existing infrastructure, as well as pave the path for migrating to Cloud solutions.

The XenDesktop architecture, FMA, adds the hybrid Cloud provisioning capability, which lets the customers use Cloud services, as well as the traditional virtual infrastructural deployments. The XenDesktop supports Cloud services with the help of a public AWS or Citrix CloudPlatform powered by Apache CloudStack Cloud for flexing, growing, or transforming virtual desktop infrastructures.

It also supports the existing hypervisors, storage, and Microsoft infrastructures, and this enables businesses to leverage their current investments, while providing the flexibility for adding or changing alternatives. Support includes all the major hypervisors, such as Citrix XenServer, Microsoft Hyper-V, and VMware ESX. It simplifies the management of networked storage by using Citrix StorageLink technology, which was leveraged and supported by XenServer. XenDesktop also closely integrates with Microsoft App-V and System Center for application management.

Citrix FMA is the XenDesktop architecture that plays a key role in Project Avalon Excalibur by converging XenApp with the XenDesktop solutions. Citrix, with XenDesktop 7.0, has converged the XenApp with XenDesktop. Now, both solutions share a common FMA architecture.

The other key benefits of the FMA architecture include:

The following figure is a diagrammatic representation of the XenDesktop FMA architecture:

To reduce the desktop management cost and complexity, XenDesktop includes the integration of a range of Citrix application virtualization technologies with on-demand applications by Citrix XenApp. With application virtualization, IT can control data access, manage fewer desktop images, eliminate any system conflicts, and reduce the application regression testing, by making it a requirement for successful desktop virtualization. Adding, updating, and removing applications has now become simple as XenDesktop now includes a self-service app store, which has been made available through the storefront, and lets users access applications instantly from any location.

The XenDesktop Platinum edition includes the Citrix AppDNA application migration technology, which simplifies app migrations to the latest versions of Windows. The Citrix AppDNA application management software combines insight about the application portfolios with an accurate application testing, compatibility, and remediation. It lets enterprises discover, automate, model, and manage the applications for migrations. It also deploys new virtualization technology and daily application management. Automating the application migration process saves enterprises time, labor, and cost, while reducing risk. It greatly helps the desktop transformations to be completed on time, within budget, and with lesser end user disruption. The AppDNA software also provides the knowledge that guides business decisions about application compatibility, migration, management, and building a long-term application portfolio evolution.

The Citrix AppDNA software simplifies the following key areas of application management:

When deploying Citrix XenDesktop within large organizations and government environments, security standards are an important consideration. Citrix is committed to making sure that the technology is fully secure and adheres to government standards for encryption and accessibility.

For businesses, XenDesktop currently offers the following security and compliance capabilities: