What's the beef here then? Well in a nutshell Diskless PCs and Vista Enterprise Centralised Desktop open up new methods for IT departments to roll out and manage their desktop estate. These new methods introduce different benefits so allow me to describe the different technologies.
The Diskless PC
Simply put this is a PC without a disk! No brainer huh? It's a PC that only has processor, memory, networking, graphics card etc whilst the machine's hard disk is located centrally in what could be a SAN or other datacenter setup. This scenario is enabled by high speed networks and reliable network infrastructure that has high QoS (quality of service) so effectively the hard disk IO travels over the wire and is processed locally by the other computer components.
Historically this kind of PC wasn't catered for under Microsoft licensing but last year with Vista we announced a new licensing scheme for enterprise customers that catered for the increased customer demand for this technology.
It's not currently a common setup but for organisations that consider security of data an absolute top priority this is a very interesting option.
Vista Enterprise Centralised Desktop (VECD)
So a slight twist on this one. VECD allows a desktop PC running Windows or a thin client machine (typically running Windows CE or Windows Embedded) to access a Virtual Machine that is stored and managed centrally on a server running Virtual Server 2005 R2 (or Hyper-V in future). In this scenario you are harnessing the server's horsepower to run the operating system and the desktop comes back to the local machine.
This capability is delivered via a subscription based licensing agreement which is an option when you buy Windows Vista Enterprise (available through Software Assurance).
What do these two technologies enable?
Scott Woodgate, Director of Windows Business Group puts it very nicely;
"They either centralize the storage of Windows, the execution of Windows, or both, in the data center."
Well, this is only a prediction but think about the next logical step. What we're seeing here is a shift to cloud based utility computing. VECD and diskless PCs are a stepping stone to this vision with an on premise solution where the processing and/or storage is done centrally in the data center.
This is only possible thanks to reliable networking internally to businesses and at present we don't have widespread high quality, high speed internet networks to facilitate this over wide area networks. Once the infrastructure is in place however these kind of experiences will be enabled.
If this kind of stuff floats your boat or you would like more detailed information on the licensing implications for this stuff I would recommend you check out this: