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A virtual machine (VM) is a software-based simulation of a computer system. It allows an operating system and associated applications to run in an isolated environment on a physical host computer as if it were a standalone, independent machine. A VM is created and managed by what is known as hypervisor software, which allocates the host’s physical resources (processor, memory, disk, network) to the virtual machine.
How does a virtual machine work?
A virtual machine (VM) works by simulating a physical computer using virtualization technology. The process starts with hypervisor software installed on the physical host computer, which acts as an intermediary between the hardware and the VM.
- The hypervisor as the basis for virtualization
The hypervisor is the software that enables VMs on a physical machine. It has two main tasks:
- Resource allocation: The hypervisor divides the host computer’s physical CPU, memory, hard disk, and other resources into “virtual” resources and allocates them to the VMs.
- Isolation and management: The hypervisor ensures that the VMs run independently from each other, so that one VM does not affect another and that the host operating system remains isolated.
There are two types of hypervisors:
- Type 1 hypervisors: Run directly on the physical server hardware (bare-metal).
- Type 2 hypervisors: Run as software within a host operating system and provide virtualization in a desktop environment.
- Creating the virtual machine
Once the hypervisor is activated, VMs can be created. A virtual machine consists of:
- Virtual hardware components: The hypervisor creates virtual versions of hardware components, such as the CPU, RAM, hard disk and network adapters.
- Virtual hard disks: Each VM has its own virtual hard disk, which is stored as a file on the host computer. This file stores the VM’s operating system, applications and data.
- Network connections: The hypervisor sets up virtual network cards that allow the VM to connect to other VMs or networks.
- Installing and running an operating system
Any operating system can now be installed on a virtual machine that thinks it is running on a real computer. Once the operating system is installed, the virtual machine behaves exactly like a physical computer on which applications can be installed and run.
- Resource utilization and management
The hypervisor manages the use of physical resources by virtual machines:
- Efficient use: Resources are dynamically allocated and adjusted as needed.
- Isolation: VMs can operate independently of each other and cannot directly affect each other.
- Prioritization: Some hypervisors allow prioritization so that critical VMs can get more resources when needed.
- Virtual networks and communication
Hypervisors also enable the creation of virtual networks through which virtual machines can communicate with each other and with the host. This is useful for environments in which multiple VMs need to interact (e.g., server networks or test environments).
- Snapshots and Migration
Most hypervisors provide snapshot capabilities that allow a VM to be saved at a specific point in time. These snapshots enable quick recovery in the event of errors.
What types of virtual machines are there?
There are two main types of VMs that serve different purposes:
System Virtual Machines
This type of VM emulates a complete computer system and allows a full operating system and applications to run in a virtual environment. System VMs provide a high level of isolation because each operating system runs within its own VM.
Process Virtual Machines
Process VMs are used specifically to run individual programs or applications. Unlike system VMs, which virtualize an entire operating system, process VMs create an isolated environment for a specific process. They run in an abstraction layer that enables cross-platform applications.
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Where are virtual machines used?
VMs have a wide range of uses in various areas of IT because they offer flexibility, security and efficiency.
Server consolidation and resource optimization
Virtual machines make it possible to run multiple virtual servers on a single physical server, reducing hardware requirements and operating costs. Consolidation enables IT departments to use hardware resources more efficiently and manage multiple workloads on a single platform.
Software development and testing
Developers use virtual machines to test software in different operating systems and configurations without affecting the host system. Because virtual machines can be created, reset, and deleted quickly, they provide a flexible testing environment for trying out new applications or updates without affecting existing systems.
Isolated and secure environments for applications
Virtual machines provide an isolated environment that ensures applications or potentially dangerous programs do not affect the host system. This isolation is particularly useful for performing security tests, running unknown programs, or sandboxing applications.
Cloud computing and hosting services
Virtual machines are the basis for many cloud computing services. Providers such as Amazon Web Services (AWS), Microsoft Azure and Google Cloud use VMs to offer flexible, scalable resources. Customers can rent virtual machines in the cloud to host applications, provide websites, and perform complex calculations.
Disaster recovery and backup solutions
Virtual machines offer simple backup and recovery options. You can create “snapshots” that store the state of the VM at a specific point in time. In the event of an outage, a VM can be quickly restored to another server, reducing downtime and ensuring business continuity.
Cross-platform compatibility and cross-platform development
Process VMs enable programs to be executed independently of the host computer’s operating system. This allows developers to create applications that work the same on different platforms (e.g., Windows, macOS, Linux).
Virtual desktop infrastructure (VDI)
VMs are used to virtually deliver desktop environments that can be accessed on any device. This method is often used by businesses to enable remote working by giving employees access to their virtual desktop regardless of their location.
Malware analysis and IT security testing
Security researchers use virtual machines to safely analyze malware and other threats without risking the host system. A VM can be easily reset if a malicious file is executed, providing a safe environment for investigation.
Continued use of old and incompatible software
Older programs that no longer work on newer systems can be run in virtual machines with an old operating system. This method is particularly valuable for companies that depend on specialized software that has not been updated.
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