Guest Operating System (Guest OS)

Definition

Guest Operating System (Guest OS) is the operating system installed inside a Virtual Machine (VM). It behaves like a normal operating system (such as Linux or Windows) but runs on virtual hardware provided by a Hypervisor, not directly on the physical hardware. Its role is to run applications and services inside a VM while sharing the physical server's resources (CPU, RAM, storage) with other Guest OSs.

What Problem It Solves

• Allows multiple operating systems to run independently on one physical server.
• Lets each VM have its own software, settings, users, and applications without affecting other VMs.
• Makes testing, hosting, and cloud deployments more flexible.

What Happens If Not Used

• A Virtual Machine cannot function because it needs an operating system to run applications.
• You would have to install the operating system directly on the physical server, limiting you to one primary OS at a time.

Easy Wording

A Guest Operating System is the operating system that runs inside a virtual computer.

Layman Example

Imagine an apartment building (physical server). Each apartment (VM) has its own family (Guest OS). Every family lives independently, even though they all share the same building.

Technical Example

** Without Virtualization **

User → DNS → Physical Server → Windows Server → Web Server → Website

Only one operating system is installed directly on the hardware.

With Virtualization

User → DNS → Physical Server → Hypervisor

→ VM 1 → Ubuntu (Guest OS) → Nginx → Website A

→ VM 2 → Windows Server (Guest OS) → IIS → Website B

→ VM 3 → Rocky Linux (Guest OS) → MySQL Database

Each Guest OS thinks it has its own computer, while the Hypervisor safely shares the physical server's hardware among all the VMs.