Cambridge A-Level Computer Science (9618) · lesson 14 of 15 · 25 min
Virtual Machines
A virtual machine (VM) is a software emulation of a complete computer system. A hypervisor (VMM — Virtual Machine Monitor) runs on the host hardware and manages one or more VMs, each with its own virtual CPU, memory, storage, and network interfaces.
Benefits of Virtualisation
Server consolidation: run multiple VMs on one physical server, reducing hardware costs. Isolation: a crash or security breach in one VM does not affect others. Snapshots: save and restore VM state instantly — ideal for testing. Portability: VMs can be moved between physical hosts. Development/testing: run multiple OS environments on one machine. Cloud computing: AWS, Azure, GCP all use virtualisation to provide IaaS.
Emulation vs Virtualisation
A Type 1 hypervisor runs:
- As an app on Windows
- Directly on the hardware with no host OS
- Inside a virtual machine
- On a cloud server only
- Answer: 1
Type 1 (bare-metal) hypervisors run directly on hardware — no host OS required.
What is the main performance difference between emulation and virtualisation?
- Emulation is faster
- Virtualisation is faster because it runs on the same architecture
- They have identical performance
- Emulation uses less memory
Answer: Virtualisation is faster because it runs on the same architecture
Virtualisation runs on the same CPU architecture, so instructions execute natively. Emulation must translate every instruction.
Which feature of VMs makes them ideal for software testing?
- They are faster than physical machines
- Snapshots allow instant save and restore of state
- They use less electricity
- They support more programming languages
Answer: Snapshots allow instant save and restore of state
VM snapshots let you save a clean state, test, then instantly revert — perfect for testing software.
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