Virtual machine

Virtual Machine

A screenshot of VirtualBox, a popular virtual machine software.

Diagram illustrating hardware virtualization.

A virtual machine (VM) is a software emulation of a physical computer that runs an operating system and applications just like a physical computer. Virtual machines are created and managed by a hypervisor, which is a layer of software that allows multiple VMs to run on a single physical machine, sharing its resources.

Overview

Virtual machines are a key component of virtualization, a technology that allows for the abstraction of computer resources. By using virtualization, multiple operating systems can run on a single physical machine, each in its own isolated environment. This is particularly useful for server consolidation, testing and development, and running applications that require different operating systems.

Types of Virtual Machines

There are two main types of virtual machines:

• System Virtual Machines: These provide a complete system platform that supports the execution of a complete operating system. Examples include VMware Workstation, VirtualBox, and Microsoft Hyper-V.

• Process Virtual Machines: These are designed to run a single program or process. An example is the Java Virtual Machine (JVM), which allows Java applications to run on any device that has the JVM installed.

How Virtual Machines Work

Virtual machines operate by using a hypervisor, which can be either a Type 1 (bare-metal) or Type 2 (hosted) hypervisor.

• Type 1 Hypervisors: These run directly on the physical hardware and manage the virtual machines. Examples include VMware ESXi and Microsoft Hyper-V.

• Type 2 Hypervisors: These run on top of an existing operating system. Examples include Oracle VirtualBox and VMware Workstation.

The hypervisor allocates resources such as CPU, memory, and storage to each virtual machine, ensuring that they operate independently of each other.

Benefits of Virtual Machines

Virtual machines offer several advantages:

• Isolation: Each VM is isolated from others, providing security and stability.
• Resource Efficiency: Multiple VMs can share the same physical resources, reducing hardware costs.
• Flexibility: VMs can be easily created, modified, and deleted, making them ideal for testing and development.
• Portability: VMs can be moved between different physical machines, providing flexibility in deployment.

Challenges of Virtual Machines

Despite their benefits, virtual machines also present some challenges:

• Performance Overhead: VMs may have a performance overhead compared to running directly on physical hardware.
• Complexity: Managing multiple VMs and hypervisors can be complex.
• Security: While VMs are isolated, vulnerabilities in the hypervisor can potentially affect all VMs.

Also see

• Virtualization
• Hypervisor
• Cloud computing
• Containerization
• Java Virtual Machine