virtual machines – Definition and meaning

Basics of virtual machines

Today, virtual machines (VMs) are an integral part of modern IT infrastructures. They enable the parallel operation of multiple, independent operating systems and applications on a single piece of physical hardware. The basis for this is virtualisation software, the so-called hypervisor, which abstracts the real resources of a computer and distributes them flexibly to various virtual instances. From the point of view of the operating system set up on it, each VM behaves like an isolated computer with its own hardware, even for the software running on it. This technology has made the management of complex IT environments - especially in data centres and development departments - much simpler and more flexible.

Functionality and architecture

The technical basis of virtual machines is the hypervisor. Two main variants are used:

• Type 1 hypervisor (bare metal): Installed directly on the hardware and offers a particularly high-performance virtualisation solution. Examples of this are VMware ESXi, Microsoft Hyper-V or XenServer.
• Type 2 hypervisor (hosted): Is based on an existing operating system and is particularly suitable for laboratories and development environments - such as Oracle VirtualBox, VMware Workstation or Parallels Desktop.

The main task of the hypervisor is to allocate and manage processor performance, memory, mass storage and network and peripheral access to the individual virtual instances. Each VM receives its own virtual hardware equipment - from network cards to hard disks and graphics cards - which appears real to the guest system. In this way, different operating systems, such as Windows, Linux or BSD, can be run in isolation and in parallel.

Companies often use management platforms such as VMware vSphere or Microsoft System Center Virtual Machine Manager to centrally control and monitor many virtual machines. Such solutions enable automated, scalable administration even with several thousand instances.

Areas of application and practical examples

There is a wide range of possible applications for virtual machines, from server consolidation to development and test environments to cloud services. Typical use cases include

• Server consolidation: several formerly physical servers run as separate VMs on just a few hosts. For example, a medium-sized company can run Exchange Server, Domain Controller and database server each in their own VMs on a single physical server.
• Development and test environments: Developers and administrators test different system variants or software updates securely and separately from each other. For example, different network topologies or release statuses can be simulated in parallel on a notebook.
• Education and training environments: Educational institutions use virtual machines for reproducible and resettable training scenarios in which participants can experiment without causing permanent changes.
• Disaster recovery & backup: Snapshots and VM clones make it easier to back up and restore entire systems. A failure can be quickly mitigated by starting a VM copy on alternative hardware or external resources.
• Cloud computing: Large cloud providers such as AWS, Microsoft Azure or Google Cloud provide scalable resources based on VMs. Companies can start, pause or delete virtual machines as required and remain flexible in their resource planning.

A practical example: If a complex web application is operated in a company, the production environment can be divided into several virtual machines - for example for the web server, database and application logic. At the same time, copies of these VMs can be used for testing and development purposes in order to try out updates and new features without any risk to live operation.

Advantages of virtual machines

Virtualisation opens up numerous possibilities that go far beyond pure cost efficiency:

• Optimised use of resources: combining several services on one hardware platform reduces idle times and cuts both power requirements and air conditioning costs.
• Maximum flexibility: Virtual machines can be installed, cloned, migrated or removed again in a short space of time - adjustments to the infrastructure can be made without physical intervention.
• Isolated environments: Each VM operates independently of others, so errors or security problems in one instance have no direct impact on other VMs.
• Reliable test and development environments: Different systems can be tested in parallel, with functions such as snapshots or rollback mechanisms ensuring fast recovery of previous system statuses.
• Efficient backup & disaster recovery: VMs are easy to back up and, if necessary, can be completely transferred to new hardware or other data centres in a short space of time.

This opens up options for providing and testing different scenarios and configurations with little effort, particularly for smaller companies and in research and teaching.

Challenges and disadvantages

In addition to numerous advantages, virtualisation also brings with it certain challenges:

• Performance overhead: The virtualisation layer takes up additional resources. This can be critical for high-performance applications and requires careful planning of the infrastructure.
• Security challenges: Although VMs are isolated from each other, vulnerabilities in the hypervisor could potentially allow access to other instances. Consistent security management for the host system remains essential.
• Licensing and compliance issues: Managing numerous cloned or migrated VMs makes it difficult to handle licences correctly and places high demands on IT compliance.
• Administrative complexity: As the number of virtual machines increases, so does the administrative effort. Without efficient tools, there is a risk of uncontrolled proliferation ("virtualisation sprawl") in the company.

Good concepts for administration and IT security help to address these challenges in a targeted manner and fully exploit the benefits of virtualisation.

Criteria for selection and operation

Efficient results in dealing with virtual machines require that all components used are selected sensibly and harmonised with each other. Decisive factors include

• Performance reserves and reliability of the hardware used - in particular CPU, main memory, network connection and storage solutions.
• Hypervisor type and range of functions: Features such as live migration, snapshots, automated backups or support for multiple clients are often required.
• Compatibility of the planned guest systems with the virtualisation environment.
• Functional diversity in administration and monitoring: Can VMs be organised and controlled centrally, clustered or deployed automatically?
• Available protection mechanisms and options for isolating individual VMs.
• Cost structure, existing licensing models and the provider's support systems.

In heterogeneous IT environments in particular, a combination of locally operated and cloud-based VMs is often the best option. Open source solutions such as VirtualBox are often sufficient for private use or smaller test environments. In the corporate environment, however, professional platforms such as VMware vSphere or Microsoft Hyper-V are established.

Outlook and current trends

Virtualisation technologies are constantly evolving in the wake of digitalisation. Container solutions such as Docker or Kubernetes are becoming increasingly important, especially for the flexible provision of modern applications and microservices based on operating system virtualisation. Nevertheless, full VM technology remains indispensable for many scenarios - for example, for complete operating system isolation or when using legacy systems with different architectures.

The concept of serverless computing and infrastructure as code is also becoming increasingly popular. Here, the provision and control of VMs, containers and other IT resources are largely automated in order to make infrastructure even more agile and efficient. However, a solid technical and administrative understanding of the underlying concepts is still required for the sustainable operation of virtual machines.

Virtual machines have fundamentally changed the design and management of IT landscapes and will continue to shape this change in the future - both in local data centres and in public cloud architectures.