A virtual machine (VM) is a software-based computer with its own virtual CPU, memory, disk and network that runs a full operating system, isolated from other VMs on the same physical host.
Why it matters
VMs allow one physical server to be divided into many independent systems, which improves hardware use and isolation. Cloud instances and VPS plans are virtual machines. You can snapshot, clone and move them between hosts.
Compared with containers, VMs are heavier because each carries a full operating system, but they provide stronger isolation and can run different operating systems side by side.
Example
One physical server with 64 cores hosts 20 VMs. One VM runs Ubuntu with nginx, another runs Windows Server with an application, and a third runs a database. A crash in one does not directly stop the others.
Common mistakes
- Overcommitting memory on the host so the VMs swap and become slow.
- Never updating the guest operating system because it is virtual.
- Taking snapshots and keeping them for months, which hurts performance and uses space.
Related
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