What is a Virtual Machine (VM)?

A virtual machine (VM) is a software-based emulation of a physical computer. It runs an operating system and applications like a physical machine. The VM operates on a physical server, known as the host, through a layer of virtualization software. This technology enables multiple VMs to share the same hardware. Each VM functions independently, with dedicated virtual resources. Virtualization is the foundation of Infrastructure as a Service (IaaS) in cloud computing. It allows efficient use of hardware, simplified management, and rapid deployment. VMs provide isolation, scalability, and portability across environments. They are essential for modern data centers and cloud platforms. By abstracting hardware, VMs enable flexible and resilient IT infrastructures.

Technical definition of a virtual machine

A virtual machine (VM) is a self-contained operating environment. It simulates a physical computer using software. The VM runs on top of a physical host system. It is isolated from other VMs and the host. This isolation applies to processes, memory, storage, and network. No VM can directly access another’s resources. The hypervisor enforces this separation.

Each VM runs its own Guest OS. This operating system is independent of the host’s OS. The Guest OS can differ in version or type. For example, a Linux VM can run on a Windows host. Applications inside the VM interact only with the Guest OS. The Guest OS communicates with hardware via the hypervisor.

A VM is often described as a “computer within a computer”. It has virtual equivalents of hardware components. These include a virtual CPU (vCPU), virtual RAM (vRAM), virtual disks, and virtual network interfaces (vNIC). From the user’s perspective, it behaves like a standalone machine. Yet, it shares physical resources with other VMs. This model enables efficient resource utilization and operational flexibility.

The Hypervisor explained

The hypervisor is the core component that enables virtualization. It creates and manages VMs on a physical host. It allocates physical resources—CPU, memory, storage, and network—to each virtual machine instance. The hypervisor schedules access to these resources. It ensures fair sharing and prevents interference between VMs. It also maintains strong isolation between VMs.

Think of the hypervisor as a “conductor” of an orchestra. Each VM is an instrument. The conductor ensures each plays at the right time and volume. Without coordination, the result would be chaos. Similarly, the hypervisor orchestrates VMs to run smoothly on shared hardware.

There are two main types of hypervisors: Type 1 and Type 2.
Type 1 hypervisors are standard in enterprise and cloud environments. They offer better performance and security. Type 2 hypervisors are common for local development and training.

Components of a virtual machine

A VM consists of virtualized hardware components. These are mapped to physical resources by the hypervisor.

The vCPU represents a share of the physical CPU. It may correspond to a core, thread, or time slice. Multiple vCPUs can be assigned to a VM. Overallocation is possible but must be managed carefully.

vRAM is the memory allocated to the VM. It comes from the host’s physical RAM. Memory overcommit is supported but can lead to swapping if overused.

Virtual disks store the Guest OS, applications, and data. They use formats like VMDK, VHD, VHDX, or QCOW2. Two provisioning models exist: thick provisioning (full space allocated at creation) and thin provisioning (space grows as needed). Snapshots capture the disk state at a point in time. They enable rollback after updates or failures.

The vNIC connects the VM to a virtual network. It is linked to a virtual switch managed by the hypervisor. Multiple vNICs can be added for network segmentation.

Gold Images or Templates are preconfigured VM images. They include an OS, drivers, and common software. Templates speed up deployment and ensure consistency. They support automation and compliance.

Key advantages of virtual machines

Isolation and Security

Each VM operates in a separate environment. A failure or breach in one VM does not affect others. This isolation enhances security and stability. It allows coexistence of untrusted or legacy applications.

Resource Consolidation and Efficiency

VMs enable server consolidation. Multiple workloads run on a single physical server. This reduces hardware, power, and space requirements. Resource utilization improves significantly. Idle capacity is minimized through dynamic allocation.

Flexibility and Operational Agility

VMs support Live Migration, moving running VMs between hosts with no downtime. Useful for maintenance or load balancing. Snapshots allow quick rollback after configuration changes. OVF and OVA formats standardize VM packaging. They enable easy import/export across platforms. VMs can be cloned, backed up, and restored rapidly.

Common use cases for virtual machines

1. Server Consolidation: Run multiple applications on fewer physical servers.
2. Development and Testing: Quickly spin up isolated environments for code testing.
3. Legacy Application Support: Run outdated software on modern hardware.
4. Disaster Recovery (DR): Replicate VMs to backup sites for fast failover.
5. Virtual Desktop Infrastructure (VDI): Deliver desktops as a service to users.
6. Cloud Migration: Lift-and-shift on-premises servers to the cloud.
7. Security Sandboxing: Analyze malware in isolated VMs.
8. Multi-OS Environments: Run Linux, Windows, and BSD on the same hardware.