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Both system virtual machines and process virtual machines date to the 1960s and remain areas of active development. System virtual machines grew out of time-sharing , as notably implemented in the Compatible Time-Sharing System (CTSS).
Full virtualization is particularly helpful in operating system development, when experimental new code can be run at the same time as older, more stable, versions, each in a separate virtual machine. The process can even be recursive: IBM debugged new versions of its virtual machine operating system, VM, in a virtual machine running under an ...
A virtual machine implements functionality of a (physical) computer with an operating system. The software or firmware that creates a virtual machine on the host hardware is called a hypervisor or virtual machine monitor. [2] Software executed on these virtual machines is separated from the underlying hardware resources.
Virtual machine instructions process data in local variables using a main model of computation, typically that of a stack machine, register machine, or random access machine often called the memory machine. Use of these three methods is motivated by different tradeoffs in virtual machines vs physical machines, such as ease of interpreting ...
There are many different process models, some of which are light weight, but almost all processes (even entire virtual machines) are rooted in an operating system (OS) process which comprises the program code, assigned system resources, physical and logical access permissions, and data structures to initiate, control and coordinate execution ...
These hypervisors run on a conventional operating system (OS) just as other computer programs do. A virtual machine monitor runs as a process on the host, such as VirtualBox. Type-2 hypervisors abstract guest operating systems from the host operating system, effectively creating an isolated system that can be interacted with by the host.
A virtual machine (VM) can be more easily controlled and inspected from a remote site than a physical machine, and the configuration of a VM is more flexible. This is very useful in kernel development and for teaching operating system courses, including running legacy operating systems that do not support modern hardware.
Operating-system-level virtualization usually imposes less overhead than full virtualization because programs in OS-level virtual partitions use the operating system's normal system call interface and do not need to be subjected to emulation or be run in an intermediate virtual machine, as is the case with full virtualization (such as VMware ...