Open-source software company Red Hat has made a bid at cloud virtualization with the release of the latest version of its operating system, which includes a built-in hypervisor. Red Hat Enterprise Linux (RHEL) 5.4, which was made available to subscribers on Wednesday, incorporates a kernel-based virtual machine (KVM) hypervisor--software that allows multiple virtual operating systems to run on a host machine or system. The company first announced its move to KVM from its previous Xen-based hypervisor strategy in June 2008, with RHEL 5.4 promised as the first production OS so equipped in February 2009.