Virtualization · Cloud & Infrastructure
Virtual Machine
Also known as: VM, Guest, Guest OS
A software-based emulation of a physical computer. Multiple VMs run simultaneously on one physical host, each with its own OS, sharing CPU, RAM, and storage through a hypervisor.
A hypervisor (VMware ESXi, Microsoft Hyper-V, KVM) sits between the physical hardware and the VMs running on it. It allocates CPU cores, RAM, storage, and network interfaces to each VM as virtual resources, while managing sharing and isolation between them.
From inside a VM, everything looks like a physical machine: a CPU, memory, disk, network card. The VM's OS doesn't know — and doesn't need to know — that it's virtualized. It installs and runs exactly like it would on physical hardware.
Why virtualization matters
Resource efficiency — a physical server with 512GB of RAM and 32 cores can run dozens of VMs that collectively utilize that capacity. Running one workload per physical server wastes most of the hardware.
Isolation — VMs are isolated from each other. A crash or compromise in one VM doesn't directly affect others on the same host.
Snapshots and cloning — take a point-in-time snapshot before a risky change; revert instantly if something goes wrong. Clone a VM to create identical environments.
Live migration — running VMs can be moved between physical hosts without downtime, enabling maintenance and load balancing.
VM performance considerations
VMs add a thin layer of overhead, but on modern hypervisors running modern hardware, this overhead is negligible for most workloads — typically 1-5% CPU overhead. For storage-intensive workloads, the I/O path (how storage is presented to VMs) matters more: NVMe pass-through or iSCSI from a fast NAS performs very differently from a shared VMFS datastore on slow HDDs.
Over-committing memory — allocating more RAM to VMs than physically exists — causes swapping and is one of the most common sources of VM performance problems in production environments.