What is a Hypervisor?
A hypervisor is software that turns one physical server into several virtual machines, giving each its own operating system, a share of CPU time, memory and disk while keeping them isolated. Type 1 hypervisors such as KVM, ESXi and Hyper-V run directly on hardware and power every VPS and cloud server.
For VPS buyers and students who want to understand what sits between their virtual server and the physical machine.
knowledge
- Read time
- 4 min
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- 7
- Updated
- 14 Nov 2026
- Written by
- WebJi® team
Last editorial update: 14 November 2026.
What a hypervisor does
A hypervisor is software that lets one physical computer run several virtual machines (VMs), each with its own operating system, by presenting virtual hardware to every guest, scheduling CPU time, dividing memory and disk, and isolating the guests from one another. It is also called a virtual machine monitor (VMM).
- Creates VMs: each guest sees its own virtual CPU, memory, disk and network card.
- Schedules CPU: physical cores are time-shared into vCPUs.
- Allocates memory and storage: the RAM and disk your plan promises are enforced here.
- Isolates tenants: one VM cannot read another's memory or files.
Every VPS and cloud instance runs on a hypervisor; KVM is the usual one on Linux hosting, including WebJi® KVM VPS plans. What that means for buyers is covered in what VPS hosting is.
Type 1 vs Type 2 hypervisors
A Type 1 (bare-metal) hypervisor runs directly on the server hardware and is what hosting providers use; a Type 2 (hosted) hypervisor runs as an application on a desktop operating system and is what developers use on laptops. The classification goes back to Popek and Goldberg's 1974 paper on virtualisation requirements.
| Type 1 (bare metal) | Type 2 (hosted) | |
|---|---|---|
| Runs on | The hardware directly | Windows, macOS or desktop Linux |
| Examples | KVM, VMware ESXi, Microsoft Hyper-V, Xen | VirtualBox, VMware Workstation, Parallels |
| Performance | Close to bare metal with hardware virtualisation | Fine for testing; host OS adds overhead |
| Isolation | Strong; no desktop OS in the path | Weaker; depends on the host OS |
| Used by | VPS, cloud and enterprise servers | Developers and labs |
KVM is a Linux kernel module that turns the kernel itself into a hypervisor, so it is usually classed as Type 1 even though a full Linux system runs on the host.
KVM, VMware ESXi, Hyper-V, Xen and Proxmox compared
KVM is the open-source default on Linux hosting, ESXi the long-standing enterprise choice, Hyper-V the Windows Server option, Xen an older open-source hypervisor still found in some clouds, and Proxmox VE a management platform built on KVM.
| Hypervisor | Licence | Typical use |
|---|---|---|
| KVM | Open source, part of the Linux kernel since 2007 | Most Linux VPS and many public clouds |
| VMware ESXi | Commercial, sold by Broadcom | Corporate data centres with vCenter management |
| Microsoft Hyper-V | Included with Windows Server | Windows-centred estates |
| Xen | Open source | Some clouds and security-focused systems |
| Proxmox VE | Open source, optional paid support | Small providers and labs; manages KVM VMs and LXC containers |
For a buyer, the practical difference is full virtualisation: on KVM your VM runs its own kernel and can use reserved RAM, unlike older container-based “VPS” products that share one kernel.
How a hypervisor divides vCPU, RAM and disk
Physical cores are time-shared into vCPUs, RAM is usually assigned to each VM as a fixed allocation, and disk is carved into virtual volumes on local or shared storage. When a plan says “2 vCPU, 4 GB RAM”, that is the configuration the hypervisor enforces for your VM.
- vCPU: a scheduled share of a physical core. Idle capacity can be shared, which is why heavily oversold hosts show “steal time” in
top. - RAM: normally reserved per VM, so another tenant's runaway process cannot take yours.
- Disk and network: shared physical devices, where the neighbour effect is most noticeable under heavy load.
Sizing your own VM is covered in how much RAM a VPS needs.
How to check which hypervisor your VPS uses
On a Linux VPS, run systemd-detect-virt; it prints kvm, vmware, microsoft, xen or none on bare metal. lscpu also shows a “Hypervisor vendor” line inside a VM.
systemd-detect-virt
lscpu | grep -i hypervisor
# On a host: does the CPU expose hardware virtualisation?
grep -cE 'vmx|svm' /proc/cpuinfo
# On a KVM host: is nested virtualisation enabled? (Y or 1 = yes)
cat /sys/module/kvm_intel/parameters/nested # Intel
cat /sys/module/kvm_amd/parameters/nested # AMDA non-zero count from the vmx|svm check means the processor has Intel VT-x or AMD-V, the hardware extensions modern hypervisors rely on for near-native speed.
Performance overhead and nested virtualisation
On a modern Type 1 hypervisor with hardware virtualisation, CPU-bound work runs close to bare-metal speed; the differences show up in disk I/O under load, very high network throughput and crowded hosts. If a workload needs every last bit of performance or the whole machine, a bare-metal server removes the layer entirely.
Nested virtualisation means running a hypervisor inside a VM, for example to test Proxmox or run an Android emulator on a VPS. It works only when the outer hypervisor exposes VT-x or AMD-V to the guest, which many providers leave disabled or enable on request, and each layer adds overhead. It suits labs and testing better than production.
Hypervisor vs containers (Docker)
A hypervisor virtualises hardware so each VM runs a full operating system, while a container such as Docker shares the host's kernel and isolates only processes, files and network. Containers start in milliseconds and pack more densely; VMs isolate more strongly and can run any guest OS.
A Linux host runs Linux containers, and a kernel flaw affects every container on that host, which is why providers use VMs as the boundary between customers and customers run containers inside their VMs. Containers are explained in what a Docker container is.
Frequently asked questions
Is a VPS the same as a virtual machine?
Yes, a VPS is a virtual machine that a hosting company runs on its hypervisor and rents to you, usually with a fixed monthly allocation of vCPU, RAM and disk plus a public IP address and root access.
Does a hypervisor make my server slower?
Only slightly for most workloads on modern hardware. Noticeable slowdowns usually come from too many busy VMs sharing the same disks or cores, not from the hypervisor itself. Watch CPU steal time and disk latency to spot an overcrowded host.
Can I choose the hypervisor when I buy a VPS?
Usually not; the provider picks it for the whole platform. Ask before buying if you need something specific, such as KVM for your own kernel or nested virtualisation. WebJi® Linux VPS plans run on KVM.
What is a virtual machine monitor?
It is another name for a hypervisor: the software that monitors and controls virtual machines, deciding which guest runs on which core and keeping each one inside its allocated memory.
Last editorial update: 15 November 2026.
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