A virtual machine (VM) is emulated computer hardware created and managed by software called a hypervisor. It behaves like a standalone computer with its own processor, memory, storage, and operating system, even though it shares physical resources with the host machine.
Virtual machines matter because they let you run multiple operating systems on one device. You could run Windows, macOS, and Linux simultaneously on a single computer without restarting. This isolation also improves security: if malware infects one VM, it cannot easily spread to others or the host system.
Common uses include:
- Testing software on different operating systems before release
- Running legacy applications that need older OS versions
- Setting up development environments without affecting your main system
- Server consolidation in data centres, where one physical machine hosts dozens of VMs
- Sandboxing untrusted programs for safe inspection
Gotchas to know: virtual machines consume significant resources (memory, storage, CPU) because they must emulate an entire operating system. A VM runs slower than native software because it adds an extra layer between applications and hardware. You need enough disk space for each VM's full operating system installation, which can require 20-100GB per machine.
Two types exist: Type 1 hypervisors (like Hyper-V or VMware ESXi) run directly on hardware and power server environments. Type 2 hypervisors (like VirtualBox or Parallels Desktop) run as applications on your existing OS and suit personal use.
When evaluating VMs for your needs, check that your computer has spare RAM and storage capacity, confirm the software you want to test runs on that VM type, and decide whether you need the isolation badly enough to accept the performance trade-off.