What is a virtual machine?
A virtual machine uses a physical computer's processor, memory, storage and network resources through software to operate as a separate computer. It can run its own operating system and applications. Several virtual machines can share one physical server.
How virtualization works
A layer called a hypervisor allocates physical resources and separates virtual machines from one another. The guest operating system uses virtual hardware, while the physical machine acts as the host. Each virtual machine can receive an allocation of memory, virtual processors and storage. Promising more resources than are physically available can cause slowdowns when workloads become busy simultaneously. A virtual disk is often stored as a file or storage volume. A snapshot makes it easier to return to an earlier state, but a snapshot on the same storage system is not an independent backup. A physical disk failure or unauthorized deletion can affect both.
Uses and management
Virtual machines support older applications, operating system experiments, training laboratories and shared server infrastructure. A developer might test software in a separate Linux environment without changing the host computer's settings. A virtual machine is not automatically secure: the guest needs updates, restricted network access and tested backup restoration. Malware testing requires special isolation; shared folders and bridged networks can create unwanted access. Unlike containers, virtual machines generally run separate operating system kernels. This provides flexibility but may increase memory requirements and startup time.