Virtual Machines

Another view is that it provides another example of a kernel API. In contrast to other kernel APIs (unix, microkernel, and exokernel), the virtual machine operating system exports as the kernel API the processor API (e.g., the x86 interface). Thus, each program running in user space sees the services offered by a processor, and each program sees its own processor. Of course, we don't want to make a system call for each instruction, and in fact one of the main challenges in virtual machine operation systems is to design the system in such a way that the physical processor executes the virtual processor API directly, at processor speed.