Hyper-V Extensibility and APIs...

Hyper-V Extensibility and APIs...

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Virtualization Nation,

It's been a while since my last post (sorry about that), but ever since we released the Hyper-V Beta a few months ago, the feedback over Hyper-V is off the charts. We're glad that folks are able to easily evaluate Hyper-V and thrilled with the overwhelmingly positive feedback. Keep it coming!

(BTW: In case you didn't hear, we made a few announcements today around interoperability today. You should check it out here...  http://www.microsoft.com/presspass/press/2008/feb08/02-21ExpandInteroperabilityPR.mspx)

With all of the big news about interoperability, it seemed like a perfect opportunity for me to point out ways that our customers and partners can build solutions with Hyper-V. Here’s a complete list with links to our virtualization managements APIs and virtual hard disk format.

Virtual hard disk format. The virtual hard disk (VHD) format is a block based format used to store the contents of a virtual machine. The virtual hard disk format is available here: http://www.microsoft.com/windowsserversystem/virtualserver/techinfo/vhdspec.mspx

Hyper-V WMI APIs. Hyper-V uses WMI APIs to create, manage, monitor, configure virtual resources. We expect the Hyper-V WMI APIs to be used widely in a variety of ways such as:

  • By third party management vendors who want to manage Hyper-V
  • By enterprises who want to integrate with an existing management solution
  • Developers who want to automate virtualization in a test/dev environments

More about WMI: Windows Management Instrumentation (WMI) is the Microsoft implementation of Web-Based Enterprise Management (WBEM), which is an industry initiative to develop a standard technology for accessing management information in an enterprise environment. WMI uses the Common Information Model (CIM) industry standard to represent systems, applications, networks, devices, and other managed components. CIM is developed and maintained by the Distributed Management Task Force (DMTF) of which Microsoft is an active participant.

The Hyper-V WMI APIs are publicly available here:


Hypercall APIs. Hypercall APIs are a programmatic interface to the Microsoft hypervisor. A few of the higher level functions include:

  • Partition management (created, delete, manage partition state)
  • Physical hardware management (system physical address space, logical processors, local APICs)
  • Guest physical address spaces
  • Intercepts. Parent partition may need to handle certain situations on behalf of a child partition
  • Virtual interrupt control.
  • Inter-partition communication
  • Partition save and restore
  • Scheduler. (set scheduler policy management for CPU reserves, caps and weights)
  • and more…

The Microsoft Hypercall Interface is publicly available here:


You may be wondering when someone would use the WMI APIs versus the Hypercall APIs. The Hyper-V WMI APIs are for creating, configuring and monitoring virtual resources while the Hypercall APIs are for very special purpose low-level work like IDE/debugger development.

Cheers, -Jeff

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