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A guest operating system (guest OS) is the operating system running inside a virtual machine (VM), together with the applications that run on it. Virtualization software provides the VM’s virtual hardware and manages how the guest OS interacts with the physical computer.
What is a guest operating system?
A guest OS is the operating-system layer inside a virtual machine. The U.S. National Institute of Standards and Technology (NIST) describes it as either a virtual machine running an OS instance and its applications, or the OS component of a VM’s execution stack. Oracle’s VirtualBox User Manual puts it simply: “This is the OS that is running inside the virtual machine.”
Examples include Windows or a Linux distribution installed in a VM. The guest OS runs its own applications and sees virtualized hardware presented by the virtualization software. It is not itself the VM: the VM is the environment that contains the guest OS and its virtual hardware.
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The guest OS runs inside the VM. In hosted virtualization, the host OS runs on the physical computer, and the hypervisor runs on top of that host OS. The host OS and guest OS can belong to different operating-system families; whether a particular guest will run successfully or receive official support depends on the virtualization product.
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| Term | What it refers to | Where it runs |
|---|---|---|
| Guest OS | The operating system and applications running as a virtualized instance | Inside the VM |
| Virtual machine (VM) | The software-defined environment, including virtual hardware, a guest OS, and applications | Managed by virtualization software |
| Host OS | The operating system beneath the hypervisor in hosted virtualization | On the physical computer |
| Hypervisor | The virtualization component that manages guest OSs and mediates their interaction with physical hardware | On the host, or as part of a different virtualization architecture |
The host-OS description applies specifically to hosted virtualization; not every virtualization architecture has a conventional host OS layer. NIST defines the hypervisor as the component that manages guest operating systems and controls instruction flow between them and physical hardware. See NIST’s guest operating system, host operating system, hypervisor, and virtual machine glossary entries.
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A virtualization product may be capable of running an OS without officially supporting or optimizing it. For example, Microsoft’s Hyper-V documentation lists supported Windows Server, Windows, and Linux guest operating systems and points to support information for FreeBSD. Compatibility depends on details such as the host version, guest version, VM generation, and integration services; consult the product’s current compatibility documentation before following version-specific instructions.
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Support responsibilities can also differ: Microsoft says it supports issues in its own operating systems and integration services, while certified third-party operating systems are supported by their vendors. For a particular guest OS, check these factors before creating or troubleshooting the VM:
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- Host operating system and hypervisor version
- VM generation or architecture
- Virtual processor and memory limits
- Required integration tools or drivers
- Which vendor handles support
Microsoft’s supported Windows guest operating systems for Hyper-V documentation gives product-specific compatibility and integration-service details. Its listed support is not a universal rule for other hypervisors or versions.
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