A computer inside a computer
You want to test a risky program. You do not want to harm your laptop. So you make a second computer inside the first one. You try the program. Then you delete the second computer, and your laptop is not changed.
This is a virtual machine: a computer made of software. People use it everywhere, from small labs to very large data centres. A data centre is a building full of servers.
Key words
| Word | What it means | Example |
|---|---|---|
| Virtual machine | A computer made of software. It runs inside a real computer. | A Windows computer inside a laptop |
| Virtualisation | Making a virtual version of a computer, or of its parts. | Ten servers on one machine |
| Host | The real computer that runs the virtual machines. | A powerful server |
| Guest | A virtual machine running on a host. | One virtual server |
| Hypervisor | The software that makes and runs virtual machines and shares the host's parts between them. | The software that starts each guest |
| Operating system | The main program that runs a computer. | Windows, Linux |
| CPU | The processor. It runs the instructions of a program. | The brain of a computer |
| Network | Computers joined together to share data. | The college network |
| Router | A device that joins networks and sends data the right way. | A home router |
| Snapshot | A saved copy of a virtual machine at one moment. You can go back to it later. | Before a risky change |
| Emulation | Making one computer act like a different one. | An old games console on a laptop |
The cells students fill in are left blank in this preview.
What can be virtual?
A virtual machine can be a client, such as a virtual PC for a student. It can also be a server, such as a web server.
The network parts can be virtual too. A virtual switch joins virtual machines together. A virtual router joins virtual networks. So a whole network, with computers, switch and router, can live inside one real computer.
Type 1 and type 2 compared
| Type 1 (no operating system below it) | Type 2 (hosted) | |
|---|---|---|
| Runs on | Directly on the hardware | On a normal operating system |
| Speed | Faster: fewer layers | Slower: more layers |
| Used for | Data centres and servers | Laptops, learning and testing |
| Example | A server in a data centre | A student laptop |
The cells students fill in are left blank in this preview.
Quick check
Have a go
Quick check
4 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.
Extra: Real hypervisors
| Type 1 (bare metal) | Type 2 (hosted) |
|---|---|
| KVM, Xen, Hyper-V, VMware ESXi | VirtualBox, VMware Workstation, Parallels |
The cells students fill in are left blank in this preview.
Extra: Ask this lab what it is
systemd-detect-virtA command for the lesson’s lab terminal. It is shown here and not run.