What Is a Hypervisor? Type 1 and Type 2 Virtualization Explained
Learn what a hypervisor does, how virtual machines use virtualized hardware, and how Type 1 bare-metal hypervisors differ from Type 2 hosted hypervisors.
A hypervisor is the software or platform layer that creates, operates, and manages virtual machines (VMs). It is also called a virtual machine monitor (VMM).
A VM is a software-defined computer environment that can run an operating system and applications. With a hypervisor, one physical computer can run multiple VMs concurrently. Each VM can have its own guest operating system and workload.
What Does a Hypervisor Do?
Virtualization is the abstraction of physical computing resources into separate virtual computing environments. The hypervisor provides each VM with virtual versions of resources such as processor time, memory, storage, and networking.
The physical computer is the host. Depending on the hypervisor type, the host may include a host operating system. Each virtual computer is a guest, and the operating system installed inside it is the guest operating system.
The hypervisor coordinates access to the physical hardware so multiple guests can operate at the same time. From inside a VM, the guest operating system generally sees a computer with a processor, memory, disks, and network devices, even though those resources are provided virtually.
| Term | Meaning | Relationship to Virtual Machines |
|---|---|---|
| Hypervisor / VMM | The layer that enables the creation and execution of VMs. | Creates, runs, and manages virtual computers. |
| Host | The physical machine; in hosted virtualization, it can also refer to the operating system supporting the hypervisor. | Provides the underlying hardware and, where applicable, the host OS. |
| Guest | A VM or the operating system running inside it. | Uses virtual resources presented by the hypervisor. |
| Host operating system | The existing OS that supports a Type 2 hypervisor. | Sits between the physical hardware and the hosted hypervisor. |
| Guest operating system | The OS installed inside a VM. | Runs independently within its VM. |
| Isolation | Separation between guests and between guests and the host. | Helps contain failures and keep workloads independent. |
How Virtual Machines Are Isolated
Isolation means that each VM is separated from the host and from other VMs. The hypervisor controls how guests access processor, memory, storage, and network resources instead of allowing one guest to directly control another guest's environment.
For example, if a test VM becomes unstable during software testing, another VM should normally continue operating independently. A guest crash should not directly crash every other guest or the underlying host.
Type 1 Hypervisors: Bare-Metal Virtualization
A Type 1 hypervisor runs directly on physical hardware rather than as an application inside a conventional desktop host operating system. It is also called a native or bare-metal hypervisor.
Its basic stack is:
- Physical hardware
- Type 1 hypervisor
- Guest virtual machines
- Guest operating systems and applications
Because the hypervisor is deployed directly on the server hardware, Type 1 virtualization is common in servers and data centers. An organization might use one physical server to run separate VMs for web services, databases, and internal applications.
Representative Type 1 products include Oracle VM Server, VMware ESX/ESXi, and Microsoft Hyper-V.
Type 2 Hypervisors: Hosted Virtualization
A Type 2 hypervisor is installed as an application on an existing host operating system. It is also called a hosted hypervisor.
Its basic stack is:
- Physical hardware
- Host operating system
- Type 2 hypervisor application
- Guest virtual machines
- Guest operating systems and applications
Type 2 hypervisors are common on desktops and laptops because users can install them like other applications. They are useful for learning, development, testing, and trying another operating system without replacing the host OS.
Representative Type 2 products include Oracle VirtualBox, Microsoft Virtual PC, VMware Server, and VMware Workstation. Oracle VirtualBox is therefore a hosted, Type 2 hypervisor: it runs on an existing host operating system and creates guest VMs within that environment.
Type 1 vs. Type 2 Hypervisors
| Characteristic | Type 1 / Bare-Metal | Type 2 / Hosted |
|---|---|---|
| Where the hypervisor runs | Directly on physical hardware. | As an application on a host operating system. |
| Host operating system requirement | Does not require a conventional host OS beneath the hypervisor. | Requires an existing host OS. |
| Software stack order | Hardware, hypervisor, guest VMs, guest operating systems. | Hardware, host OS, hypervisor application, guest VMs, guest operating systems. |
| Typical environment | Servers, data centers, and consolidated production workloads. | Desktop testing, learning, development, and application experiments. |
| Representative products | Oracle VM Server, VMware ESX/ESXi, and Microsoft Hyper-V. | Oracle VirtualBox, Microsoft Virtual PC, VMware Server, and VMware Workstation. |
Neither type is universally best. A Type 1 hypervisor is a natural choice when an organization deploys a dedicated virtualization platform on server hardware. A Type 2 hypervisor is often more convenient when a user needs VMs on a normal desktop operating system.
Practical Examples
Desktop Operating-System Testing
A user installs Oracle VirtualBox on Windows or installs it on Linux, then creates separate Linux and Windows guest VMs. The host OS remains available while the user learns, tests applications, or compares operating systems. This demonstrates a Type 2 hypervisor, a host operating system, multiple guests, and VM isolation.
Server Consolidation
An organization installs a bare-metal hypervisor on a physical server and creates separate VMs for a web service, database, and internal application. The workloads share the server hardware while remaining logically separated. This demonstrates Type 1 virtualization and workload isolation.
Guest Failure Containment
Suppose one test VM becomes unstable after experimental software is installed. The hypervisor's isolation mechanisms are intended to let other VMs continue operating independently. However, a full host failure or a lack of shared resources can still affect several guests.
Why Hypervisors Matter
The hypervisor enables different operating systems to run on one physical computer. This supports workload separation, safer experimentation, more efficient use of hardware, and simpler software testing.
For example, a developer can use a desktop host OS while running a Linux VM for server testing. A data center can place separate application workloads in separate VMs instead of assigning one physical server to each workload.
To explore the desktop virtualization workflow, see how to create a virtual machine and install a guest operating system.
Common Misunderstandings
A VM Is Not the Same as a Hypervisor
A VM is the virtual computer. The hypervisor is the layer that creates and runs that virtual computer. For example, a Linux VM may run inside Oracle VirtualBox; the VM and VirtualBox are different parts of the system.
Type 1 and Type 2 Do Not Describe Guest OS Versions
The type describes where the hypervisor is placed in the computing stack. Type 1 runs directly on hardware, while Type 2 runs on a host operating system.
A VM Crash Does Not Normally Crash Every VM
Isolation is intended to prevent an individual guest failure from directly disrupting other guests. Nevertheless, host resource exhaustion, host operating-system failures, hardware faults, and configuration errors can affect multiple VMs.
Key Points
- A hypervisor, also called a VMM, creates, runs, and manages virtual machines.
- One physical computer can run multiple VMs concurrently.
- The hypervisor presents virtual processor, memory, storage, and networking resources to each guest.
- Type 1 hypervisors run directly on hardware and are common in server environments.
- Type 2 hypervisors run as applications on host operating systems and are common on desktops.
- Isolation helps separate guests from one another and from the host, but it does not eliminate every security or resource risk.
- The right hypervisor type depends on the workload, platform, and deployment environment.