Virtual Machines (VMs): Meaning, Working, Types, Advantages, Disadvantages & Applications

What is a Virtual Machine?

A Virtual Machine (VM) is a software-based environment that behaves like a physical computer. It contains virtualized components such as a CPU, memory, network interface, and storage. These resources are abstracted from the actual hardware by a software layer called the hypervisor, which allocates system resources to the VM.

The physical computer on which the hypervisor runs is called the host machine. The virtual machines operating on the host are called guest machines. To the hypervisor, all hardware resources—CPU, RAM, storage, and network—appear as a pool that can be dynamically assigned to VMs.

Multiple VMs can coexist on a single physical server while remaining isolated from one another. They can even be migrated between host servers depending on performance needs or resource availability. Because of virtualization, multiple operating systems can run simultaneously on a single machine—for example, a Linux distribution running inside macOS. Each OS operates just like it would on dedicated hardware, giving the user an almost identical experience.

How Does a Virtual Machine Work?

Virtualization creates a software-based computer by borrowing hardware resources from a physical machine or a cloud server. A VM is essentially a computer file—often called an image—that functions like a real system with assigned CPU, memory, and storage.

A VM may run:

• As a separate full-screen operating system
• Inside a window as a secondary environment

Since the VM is isolated from the host machine, any software running inside the VM cannot directly affect the host’s operating system. This makes VMs extremely useful for testing, development, and malware isolation.

Types of Virtual Machines

Virtual machines are broadly classified into two categories:

• Process Virtual Machines
• System Virtual Machines

1. Process Virtual Machine

A process virtual machine supports a single process and provides a platform-independent execution environment by hiding details of the underlying OS or hardware. The best example is the Java Virtual Machine (JVM), which allows Java applications to run on any operating system as if they were native.

2. System Virtual Machine

A system virtual machine provides full virtualization and replaces a physical computer. Multiple VMs can run on a single host, each with its own operating system. This type relies on a hypervisor, such as VMware ESXi or KVM, which may run directly on hardware or on top of a host operating system.

Advantages of Virtual Machines

• Multiple operating systems can run on a single hardware system, saving cost, time, and physical space.
• Useful for running legacy applications without needing to migrate them to new platforms.
• Developers use VMs to test software in a safe and isolated sandbox environment.
• VMs allow testing on new OS versions without purchasing new hardware.
• Malware is contained within the VM and cannot harm the host system.

Disadvantages of Virtual Machines

• Running multiple VMs on one physical host may cause performance issues if resources are insufficient.
• VMs are generally slower than traditional physical systems due to virtualization overhead.
• If the host machine crashes, all running VMs also stop working.
• Requires careful resource planning to avoid overload or bottlenecks.

Applications of Virtual Machines

• Running a different operating system in a window on a desktop or laptop.
• Executing software that requires a separate OS environment.
• Testing applications safely in isolated environments.
• Server virtualization to consolidate hardware usage and improve efficiency.
• Handling dangerous tasks like opening virus-infected files without risking the host.
• Cloud computing environments where VMs run server workloads.