What is Virtual Machine?
A software-emulated computer running its own full operating system on shared physical hardware.
Definition
A virtual machine runs a complete guest operating system on virtualized hardware managed by a hypervisor—Type 1 running directly on bare metal (ESXi, Xen, KVM), Type 2 running atop a host OS (VirtualBox, VMware Workstation). Because each VM includes its own kernel, isolation is strong and the boundary is a well-understood security perimeter, but boot times run to tens of seconds and memory overhead is measured in gigabytes. Containers share the host kernel instead, which is why they start in milliseconds and pack far denser—the tradeoff is a weaker isolation boundary. The two are complementary in practice: most managed Kubernetes clusters schedule containers onto pools of VMs, and technologies like Firecracker microVMs narrow the gap by booting a minimal VM in around a hundred milliseconds.