A virtual machine is a computing resource that uses software instead of a physical computer to run programs and deploy applications. It operates by running one or more virtual “guest” machines on a physical “host” machine, with each virtual machine functioning independently and running its own operating system. This means that different operating systems can coexist on the same host; for example, a virtual MacOS machine on a physical PC.
The impact of virtual machines on businesses is significant. They enable organizations to run multiple operating systems on a single computer, leading to savings in physical space, time and management costs. Virtual machines are used for a variety of purposes, including accommodating different processing power needs, running software that requires a different operating system, and testing applications in a safe and isolated environment. They have been widely adopted for server virtualization, allowing IT teams to consolidate computing resources and improve efficiency. Virtual machines also facilitate tasks that may be considered risky in a host environment, such as accessing virus-infected data or testing operating systems, as the software within the VM cannot tamper with the host computer.
Virtual machines are commonly used in combination with a hypervisor, which manages the virtualization process and allows physical resources to be shared. Additionally, VMs are often used alongside containers, another form of virtualization technology. Containers have less overhead than virtual machines, as they package a single application along with its dependencies, making them lightweight and faster to boot. However, virtual machines offer the benefits of complete isolation with their own operating systems, making them suitable for running multiple applications together, for supporting legacy applications and for scenarios requiring strict app isolation.
Container vs. Virtual Machine
Like virtual machines, container technology such as Kubernetes operates by running isolated applications on a single platform. However, there are key differences between containers and virtual machines.
Containers package up a single application along with its dependencies, while virtual machines virtualize the hardware layer to create a complete “computer” with its own operating system. Containers share the underlying host’s operating system services and isolate applications using virtual memory hardware. This leads to smaller container sizes, faster boot times and efficient resource utilization. Containers are ideal for use cases such as web applications, DevOps testing, microservices and maximizing app deployment per server.
Virtual machines are larger and slower to boot than containers. They provide logical isolation by running separate operating system kernels for each virtual machine, offering the benefits of a completely independent operating system. Containers and virtual machines can also be used together to leverage the advantages of each technology in a complementary manner.
Types of Virtual Machines
The two main types of VMs are process virtual machines and system virtual machines.
Process virtual machines enable a single process to run as an application on a host machine, providing a platform-independent programming environment by abstracting the underlying hardware or operating system. Notable examples include the Java Virtual Machine, which allows Java applications to run on various operating systems, and the common language runtime in the .NET Framework.
System virtual machines fully virtualize the underlying hardware, substituting for a physical machine. They enable the sharing of a host computer’s resources among multiple virtual machines, with each running its own instance of the operating system. System virtualization relies on a hypervisor, which can operate directly on bare hardware or on top of an existing operating system.
Pros and Cons of Virtual Machines
Virtual machines have several advantages and disadvantages compared with physical machines.
Advantages of Virtual Machines:
- Multiple operating system environments can run on a single physical computer, saving space, time and management costs.
- Virtual machines can host legacy applications, reducing the expense of migrating to a new operating system.
- They provide integrated disaster recovery and application provisioning options.
- Virtual machines enable isolated testing of risky tasks, such as accessing virus-infected data and testing operating systems.
Disadvantages of Virtual Machines:
- Running multiple virtual machines on one physical machine without meeting infrastructure requirements may lead to unstable performance.
- Virtual machines are generally slower than full physical computers.
Most enterprises adopt a combination of physical and virtual infrastructure to balance the advantages and disadvantages. Understanding the distinctions between containers and virtual machines, the different types of virtual machines, and the pros and cons of virtual machines is crucial for making informed decisions about infrastructure deployment and optimizing resource utilization.