Virtual Machines and Operating Systems โ 10 Minutes of OS, Day 18
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Before getting started ๐
What if you could run several operating systems on one computer at the same time?
Virtual machines
make that possible and are a key foundation of modern cloud computing.
This post walks through virtualization, virtual-machine architecture, hypervisors, hardware support, and the advantages and disadvantages.What is virtualization? ๐
Virtualization uses software to divide and emulate a physical computer's resources.
Virtual-machine architecture ๐
A virtual machine places a software layer above real hardware, allowing an
independent operating system
to run on top.Components ๐
- Host OS: The operating system running on the physical computer.
- Hypervisor (VMM): The software layer that manages virtual machines.
- Guest OS: An operating system running in a virtual environment.
If you run VirtualBox on Windows and install Linux, the host OS is Windows and the guest OS is Linux.
Types of hypervisors ๐
A hypervisor is the core component that creates and manages virtual machines.
1. Type 1 (bare metal) ๐
- Runs directly on hardware.
- Offers high performance and suits server environments.
- Examples: VMware ESXi and Microsoft Hyper-V (bare metal).
2. Type 2 (hosted) ๐
- Runs on a conventional operating system.
- Easy to install and use; suitable for personal computers.
- Examples: VirtualBox and VMware Workstation.
Think of Type 1 as selling products in a factory-operated store, and Type 2 as selling through a shop inside a dealer's premises.
Hardware-assisted virtualization ๐
Virtualizing access to basic resources such as CPU and memory also requires substantial computation.
To help,
modern CPUs directly support virtualization instruction sets such as VT-x and AMD-V
.- Intel VT-x and AMD-V: CPU-level virtualization support.
- SR-IOV and IOMMU: Used for virtualizing network and I/O devices.
Advantages and disadvantages of virtual machines ๐
Advantages ๐
- Run several operating systems and services on one server โ Better resource utilization.
- Provide independent environments โ Useful for testing and development.
- Isolate failures โ A failure in one environment does not affect the others.
Disadvantages ๐
- Overall performance is lower than on a physical machine.
- Sharing hardware resources can cause performance variation.
- Initial setup and management may involve costs.
Summary ๐
Virtual machines separate operating systems and resources to make efficient use of one physical device.
Because they underpin cloud, server, and development environments, understanding their structure and operation is useful.
The next post covers
networks and distributed systems
.References ๐
- Operating System Concepts (10th Edition)
- https://en.wikipedia.org/wiki/Virtual_machineโ
- https://learn.microsoft.com/en-us/virtualizationโ