Relative newcomer Convirture holds that it is plugging a major hole by specializing in managing open-source Xen, KVM virtualization and private cloud deployments. - VMware's ESX hypervisor and its vCenter control suite are thought to be operating in more than 80 percent of all enterprise IT systems. And some IT people believe that number is too conservative. Microsoft's Hyper-V, still getting its bearings in the market, is growing in use but its market sh...