With all this talk about virtualization darling VMware (its record quarter, its fawning suitors), we'd nearly forgotten there were other pretenders to the throne. Said pretenders include Microsoft, which just began public trials of Hyper-V. Hyper-V is the official name of Microsoft's long-awaited "Viridian" hypervisor, whose release has already been delayed a couple of times -- bumped from Q1 2007, to Q3, to nowheresville. But according to Fortune, Hyper-V's software will appear in three editions (there will be eight) of Windows Server 2008, with the first public release slated for Q1 2008. Windows Server 2008 Standard, Enterprise and Datacenter will include Hyper-V by default.On Standard, users may run one instance of Hyper-V per server license. Enterprise permits four runs per server license, and Datacenter clients may run unlimited instances. There will also be three editions of these packages without Hyper-V, and two separate editions of Windows Server 2008, also without Hyper-V (plainly dubbed Windows Server 2008, and Windows Server 2008 for Itanium-based Systems). Hyper-V sets Microsoft in direct competition with VMware. The biggest concern by far is whether Microsoft will choose to include it as a free feature in its product suite. That's not to say Hyper-V is the only threat to VMware's reign as virtual marauder. If you're iffy about a Microsoft offering and feel disinclined to spend money on VMware, you may do as many of VMware's rivals (including HP, Sun and IBM) have done: make use of the Xen hypervisor, a virtualization platform with open source roots.