The next step up in power for end users and step down in cost and resource conservation for IT from Web apps or terminal services. Rather than having many users share one instance of the same application or operating system, the server hosts an entire operating system and set of applications within a virtual machine that is accessible only to that user. The VM could run on a server, sharing resources with other dedicated VMs, or could run by itself on a blade PC. Can either be hosted remotely or streamed. In the streamed scenario, both applications and operating systems can be streamed to the client-downloading parts of the software as the user requires them, and executing on the client machine, using its processing power but not local storage.
Hosted remotely: Advantages: Can run applications that balk at running in shared mode; isolates activity of each user to prevent resource constraints.
Disadvantages: Uses far more bandwidth than shared desktops, and far more hardware on the server. Performance still depends on the quality of the network connection and ability of the display protocol to handle graphics. Does not work when disconnected.
Example vendor offerings: Citrix XenDesktop; Wyse ThinOS; VMware View; Microsoft Remote Desktop Services; Microsoft Enterprise Desktop Virtualization (MED-V)
Streamed: Advantages: Often gives the end user better performance because demanding graphic or other operations execute locally.
Disadvantages: Requires more powerful client hardware, reducing the cost benefit of virtual desktops. Does not work when disconnected.
Example vendor offerings: Citrix XenDesktop, XenApp, XenProvisioning; Wyse TCX; VMware View Manager, ThinApps, Composer; Microsoft VDI suite.
4. Local Virtual Applications:
Think "Java." Applications download from the server to the client machine and run there, using local memory and processing power. But they run within a "sandbox" that enforces a set of rules on what the local machine can do and to what it can connect.
Advantages: More computing resources and sometimes better performance than remotely hosted applications; less bandwidth consumption; can be used offline.
Disadvantages: Less control by IT over the hardware and security of the data.
Example vendor offerings: Citrix XenApp, Wyse TCX, VMware ThinApp, Microsoft Application Virtualization.
5. Local Virtual OS:
Present in two major versions. Option one: A client-side hypervisor can create a virtual machine within a laptop or desktop computer, which can function as a completely standalone unit that keeps itself separate from hardware and software on the client machine outside of the VM. Option two: A hypervisor runs on the machine's BIOS, allowing the user to run multiple operating systems with no "host" OS at all.
Advantages: Multiple OSes on a single system; no concerns about OS compatibility, can run on non-traditional VM clients such as smartphones or PDAs.
Disadvantages: Potential conflict for resources, relative immaturity of client-side hypervisors leaves security unproven.
Example vendor offerings: Citrix Dazzle and Receiver, Wyse PocketCloud, TCX, VMware View Client Virtualization with Offline Desktop (Experimental); Microsoft VDI suite.
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