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The desire to run multiple operating systems was the initial motive for virtual machines, so as to allow time-sharing among several single-tasking operating systems. In some respects, a system virtual machine can be considered a generalization of the concept of virtual memory that historically preceded it.
Operating-system-level virtualization, also known as containerization, refers to an operating system feature in which the kernel allows the existence of multiple isolated user-space instances. Such instances, called containers, [ 25 ] partitions, virtual environments (VEs) or jails ( FreeBSD jail or chroot jail ), may look like real computers ...
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. [8]
A hypervisor is an operating system that runs a virtual machine. The virtual machine is unaware that it is an application and operates as if it had its own hardware. [14] [29] Virtual machines can be paused, saved, and resumed, making them useful for operating systems research, development, [30] and debugging. [31]
Attempts by the guest operating system to access the hardware are routed to the virtual device driver in the host operating system as e.g., function calls. The virtual device driver can also send simulated processor-level events like interrupts into the virtual machine. Virtual devices may also operate in a non-virtualized environment.
It is a device file (it can be made with mknod for instance), but does not reference any hardware. DOS-, Windows- and OS/2-like operating systems define the NUL device that performs a similar function (but is implemented as part of the file name processing – no actual file exists by that name).
A software appliance is a software application combined with just enough operating system (JeOS) to run optimally on industry-standard hardware (typically a server) or in a virtual machine. [1] It is a software distribution or firmware that implements a computer appliance. [2] [3] Virtual appliances are a subset of software appliances. The main ...
OS-level virtualization is an operating system (OS) virtualization paradigm in which the kernel allows the existence of multiple isolated user space instances, including containers (LXC, Solaris Containers, AIX WPARs, HP-UX SRP Containers, Docker, Podman), zones (Solaris Containers), virtual private servers (), partitions, virtual environments (VEs), virtual kernels (DragonFly BSD), and jails ...