Microsoft today announced that it will extend the Open Specification Promise to the hypercall application programmer’s interface (API) within Windows Server virtualization (codename Viridian), and will be available when Windows Server virtualization is released to manufacturing (RTM). In the interim, today Microsoft posted an updated draft of the hypercall API to Microsoft’s website so that partners can continue to have early access to this important development interface. Microsoft first distributed hypercall API draft documentation to attendees of Windows Hardware Engineering Conference 2006.