The hypervisor software has the following implementations.
In the first implementation, the hypervisor software runs directly on a hardware platform, as an OS control program. A guest operating system runs at the second level above the hardware. For example, the Oracle VM server software runs directly on the hardware.
In the second implementation, the hypervisor software runs within the host operating system environment. A guest operating system runs at the third level above the hardware. For example, the Oracle VM VirtualBox software runs on the Oracle Solaris OS, the Microsoft Windows OS, and the Linux OS.