<P> As mentioned above, the VM control program includes a hypervisor - call handler that intercepts DIAG ("Diagnose", opcode x'83') instructions used within a virtual machine . This provides fast - path non-virtualized execution of file - system access and other operations (DIAG is a model - dependent privileged instruction, not used in normal programming, and thus is not virtualized . It is therefore available for use as a signal to the "host" operating system). When first implemented in CP / CMS release 3.1, this use of DIAG provided an operating system interface that was analogous to the System / 360 Supervisor Call instruction (SVC), but that did not require altering or extending the system's virtualization of SVC . </P> <P> In 1985 IBM introduced the PR / SM hypervisor to manage logical partitions (LPAR). </P> <P> Several factors led to a resurgence around 2005 in the use of virtualization technology among Unix, Linux, and other Unix - like operating systems: </P> <Ul> <Li> Expanding hardware capabilities, allowing each single machine to do more simultaneous work </Li> <Li> Efforts to control costs and to simplify management through consolidation of servers </Li> <Li> The need to control large multiprocessor and cluster installations, for example in server farms and render farms </Li> <Li> The improved security, reliability, and device independence possible from hypervisor architectures </Li> <Li> The ability to run complex, OS - dependent applications in different hardware or OS environments </Li> </Ul>

Why are type-1 hypervisors more efficient than type-2 hypervisors