Virtual Machines

Question 1

What does a virtual machine do?

Answer 1

Abstracts over the hardware of a single computer, providing multiple execution environments.

Question 2

What are the types of virtualisation?

Answer 2

• Native/ Bare Metal
• Hosted/ Embedded
• Emulation

Question 3

How does Native virtualisation work?

Answer 3

Hypervisor running directly on hardware.

Multiple OS images can be hosted

Question 4

How does Hosted emulation work?

Answer 4

Host OS has a VM manager built-in

Question 5

How does emulation work?

Answer 5

Interpreted, emulates a different machine

Question 6

How are VM’s implemented?

Answer 6

VM instance hosts an OS. This is executed in user mode.

Emulates some or all of the instruction set of virtualised HW.

Question 7

How does a virtual machine manager work?

Answer 7

Executes in privileged mode.

Interfaces with system hardware.

Privileged operations cause a trap to the VMM from VM.

Question 8

VM Pros

Answer 8

Improved hardware utilisation.

Flexibility (Largely, hardware independent).

Protection throughisolation

Question 9

VM cons

Answer 9

No direct sharing of resources (can be done in SW)

Performance penalties, sharing physical HW and emulation of some or all instructions.

Question 10

Uses of VMs

Answer 10

Infrastructure provisioning

Software compatibility

Systems development (OS development or research, testing)