What is a Virtual Machine?

A Virtual Machine (VM) is like a computer inside your computer. Imagine you're a developer who needs to test software on Windows, but you're running macOS — or you want to run an isolated Linux server without touching your host system. A VM lets you spin up a full operating system (OS) in a sandboxed environment, without needing new hardware.

Think of it as a box-within-a-box: it acts like a real machine, but it's just software.

What It Is — Technically:

A virtual machine is a software emulation of a physical computer. It runs an operating system and applications just like a physical machine does. The virtualization layer — called a hypervisor — allocates slices of your system's actual hardware (CPU, memory, disk) to these virtual environments.

There are two types of hypervisors:

• Type 1 (bare metal): Runs directly on hardware (e.g., VMware ESXi, Microsoft Hyper-V)
• Type 2 (hosted): Runs on top of another OS (e.g., VirtualBox, VMware Workstation)

How It Works:

1. You install a hypervisor
2. You configure a VM: choose its OS, disk size, memory, CPU, etc.
3. The hypervisor starts the VM as a process on your machine
4. From inside, it behaves like a separate, fully functioning computer

Key Features:

• Isolation: VMs don't interfere with the host system or other VMs
• Flexibility: Run multiple operating systems on a single machine
• Snapshotting: Save the exact state of a VM and roll back if needed
• Portability: Move or clone VMs across environments

Why Devs and Ops Teams Use VMs:

• Safely test untrusted code or environments
• Run old software that depends on outdated OS versions
• Spin up temporary infrastructure for CI/CD pipelines or load testing
• Package development environments for teams

Limitations:

• Performance Overhead: VMs are heavier than containers (like Docker)
• Boot Time: VMs take longer to start compared to containers
• Resource Usage: Each VM requires its own OS image, memory, and storage

VM vs Container:

VMs emulate entire operating systems. Containers (e.g., Docker) share the host OS kernel but isolate applications. VMs are more isolated and secure, while containers are faster and more lightweight. You often choose one over the other based on the trust boundary and performance requirements.

VMs helped define cloud computing. AWS EC2, for example, was built entirely on virtual machines for years — allowing thousands of users to share physical servers safely and predictably.