Operating System View as a Virtual Machine | OS Tutorials

The operating system is made up of layers, and this layered approach is taken to its logical conclusion in the concept of a virtual machine. Let’s understand how the operating system can work as a virtual machine.

Operating System as a Virtual Machine

Conceptually, a computer system is made up of layers. The hardware is the lowest layer in all such systems. The kernel runs at the next level, using hardware instructions to implement a set of system calls for use by outer layers. The system programs above the kernel can therefore use either system calls or hardware instructions. The system programs are at a level higher than that of the other routines; the application programs may view everything under them in the hierarchy as though the latter were part of the machine itself.

• The layered approach is taken to its logical conclusion in the concept of a virtual machine. The VM operating system for IBM systems is the best example of the virtual machine concept.
• By using CPU scheduling and virtual-memory techniques, an operating system can create the illusion of multiple processes, each executing on its own processor with its own (virtual) memory.
• Normally, the process has additional features, such as system calls and a file system, which are not provided by the bare machine.
• The virtual machine approach does not provide any additional function, but rather provides an interface that is identical to the underlying bare machine.
• Figure 1 shows the concept of virtual and nonvirtual machines. Each process is provided with a (virtual) copy of the underlying computer.

• The Resources of the physical computer are shared to create the virtual machines. CPU scheduling can be used to share the CPU and to create the appearance that users have their own processor.
• A major difficulty with the virtual-machine approach involves disk systems.
• The virtual machine concept has several advantages, such as complete protection of the various system resources. Each virtual machine is completely isolated from all other virtual machines, so there are no security problems.