Simple definition
The hypervisor shares the resources of a physical server between several virtual machines.
Technical definition
A Type 1 hypervisor runs directly on the hardware, while a Type 2 operates over an operating system. VMware ESXi, Hyper-V and Proxmox VE are common examples.
- Physical server CPU, RAM, disk and network
- Hypervisor Resource control and isolation
- Virtual resources vCPU, vRAM, virtual disks
- Virtual machines Independent guest systems
A Type 1 hypervisor runs directly on physical hardware; guest availability also depends on the host, network and storage.
What is it used for ?
Manage VMs, their virtual networks, their storage and resource allocation.
Practical example
The administrator increases the memory of a VM and moves it to another host from the hypervisor console.
Common issues
- Unique host without reddonnce
- Unapplied
- Insufficiently protected administrator access
- Shared storage unavailable
What a hypervisor actually virtualizes
A hypervisor presents logical resources to virtual machines: virtual CPUs, memory, disk controllers, network adapters and other virtual devices. Each VM runs a guest operating system that behaves much like a dedicated computer. In practice, several guests share the physical CPUs, RAM, storage and network interfaces of one host. This consolidation can reduce hardware requirements but needs careful resource planning.
Isolation between virtual machines matters, yet it does not eliminate every software vulnerability or administrative mistake. The security of the hypervisor, host management interfaces and virtual networks remains essential.
Type 1 vs Type 2 hypervisors
- A Type 1 hypervisor runs on physical hardware or in a dedicated virtualization architecture; VMware ESXi, Hyper-V and the KVM virtualization layer used by Proxmox VE are examples with different implementations.
- A Type 2 hypervisor runs as an application on top of a general-purpose host operating system, as in some desktop virtualization products.
- Virtual disks and virtual switches connect guests to storage and to physical or isolated networks.
- Live migration, high availability and replication are not universal hypervisor features; their availability depends on platform, networking, storage and licensing.
- Overcommitting vCPU or memory can work within limits, but cannot create additional physical capacity.
Virtual machines, snapshots and backups are different
A VM is a running computing environment. A snapshot records selected parts of its state at a point in time, often through delta disks. It may depend on a parent disk rather than being independently recoverable. A backup must support recovery of machine data under the organization’s recovery plan and with sufficient independence from production.
Running eight business servers on one host simplifies hardware management but concentrates operational risk. Resilience then depends on properly sized resources, reliable storage, tested backups, monitoring and—where needed—multiple hosts.
Related terms
Key takeaway: hypervisors share and isolate resources among VMs; they do not replace backups, capacity planning or high-availability design.