Virtual Machines and Guest Operating System

Virtual Machines and Guest Operating System

Author Name : Sayed Ali Akhtar Rizvi

ABSTRACT

Virtual memory is a function provided by many operating systems where the operating system creates a virtual memory space that applications can access as if it were a single piece of contiguous memory. This virtual memory space can be a combination of actual physical memory as well as disk-based resources concert. Most operating systems have a method to configure their virtual memory and, in this context, they're typically referring to the amount of disk space to allocate for virtual memory use. Swapping uses virtual memory to copy contents in primary memory (RAM) to or from secondary memory (not directly addressable by the CPU, on disk). Swap space is often a dedicated disk partition that is used to extend the amount of available memory. If the kernel attempts to access a page (a fixed-length block of memory) stored in swap space, a page fault occurs (i.e., the page is not located in RAM), and the page is "swapped" from disk to RAM.

In computing, a virtual machine (VM) is the virtualization/emulation of a computer system. Virtual machines are based on computer architectures and provide functionality of a physical computer. Their implementations may involve specialized hardware, software, or a combination. Virtualization technology allows a computer to run more than a single OS at the same time. A guest OS on a virtual machine can be different from the host OS while a guest OS on a partitioned disk must be the same be the same as the host OS. For example, if the host OS is running Windows, then any guest OSes on a partioned disk must also run windows. In a virtualized environment, the guest OS can be different than the host OS. A guest OS is required before a virtual machine can be deployed.