From Presentation Server 4.5 to XenApp 6.5 there are significant changes as you might suspect.  Let’s take a look at some of those important changes that make upgrading desirable.

Microsoft Group Policy can be used to configure provisioned servers on the fly and even reconfigure them as needed.  With the group policy integration it allows for granular control of applications and their availability.

HDX for Flash v 2 is added with Xenapp 6.5 only.  HDX offload was added in version 5 and improved on the 6 platform. HDX codecs for audio improve bandwidth use by 90% without reducing quality.  Also, a major functionality advantage with softphone support and Office communicator (now Lync) were introduced, allowing these features to move into the datacenter.  Also, the use of USB device true pass through capabilities allowing for Webcams, digital cameras and many other POS devices to be functional in the Citrix environment.  Needless to say HDX truly grew up in the XenApp 6 platform.

Streamed App Acceleration now allows for reduced launch times for subsequent launches of a streamed app.  This can cut overhead on servers that have streamed applications and kill boot storms on resources.  This addition is a big move in the right direction for a component that has been problematic and hard to unencumber.

System Center Operations Manager now allows for publishing applications to end users and image maintenance for Xenapp 6.5.  For many enterprise environment being able to fully realize their SCOM investment in relationship with the Citrix environment is very valuable.

Session Prelaunch and linger are two new features only available in 6.5.  Prelaunch creates an open ICA connection at startup using receiver.  This stream is then used when a user launches any XenApp application to reduce connection time.  Session linger works on the opposite end of the session in that a disconnected session will linger and allow another session to be created using the still open connection.

Multi-Stream ICA is only available in 6.5.  It allows for up to 4 TCP/IP streams to be used.  This is beneficial for QOS of Audio and video being delivered to the end device.

Printing is vastly improved in 6.5.  The universal print driver was rebuilt and total bandwidth consumption for printing is reduced by up to 90%.

Preferential load balancing is available from 5.0 on but is only available on the 2008 platform.  What this does essentially is allow more granular load balancing by users and groups that need priority to resources.  This could be huge for environments that have resource intensive users.

Profile management is greatly aided by profile data capture which prevents profile corruption by storing changes in the registry.  Profile streaming adds use as needed instead of loading upfront capabilities to the user profile, making large profiles more manageable.  Other profile management improvements include the ability to include or exclude files from the profile. Extended synchronization allows administrators to sync data from applications that do not store to the users profile but somewhere on the hard drive.   Folder redirection for my documents is also added with the 6 platform, and improved logging capabilities.

Secure streaming of applications is not available in Presentation Server 4.5.  Secure HTTP is an important consideration to traffic security for some environments.

Kerberos authentication is not available in 4.5 and neither is RADIUS 2-factor authentication.  This alone may be a reason for upgrading.

Xenserver virtualization platform is available only above 4.5.  This hypervisor platform opens a world of additional options and is cost effective at the price of nothing.  This alone may be enough to support a move from Presentation Server 4.5.

The Desktop Director is only available for XenApp 6.5.  This integrated management tool allows for enterprise troubleshooting, and monitoring that could not be performed from a single console before.

The ability to create servers as Controllers or Workers also is a big step towards resource management and efficiency.  This function is only available by going to 6.5 and allows for servers to either be what we generally refer to as management or as Citrix now calls controller servers.  This eliminates much of the management overhead as well from the worker servers that are better known as application servers or desktop servers.  The actual workhorses of the environment taking the user load.