A hypervisor is a process that helps separate the operating system and running applications from the hardware component. This typically refers to specialized software. However, embedded hypervisors also exist. These are available from the start, rather than being launched after system deployment.
The hypervisor is what enables the development of the virtualization concept. Hardware virtualization is the ability to manage multiple virtual machines (VMs) on a single device. They become guest systems.
An example of virtualization in use is renting a virtual server from a hosting provider. Multiple isolated spaces are located on one device. Different software can be installed on them. This increases resource utilization efficiency. Memory, computing power, and bandwidth are distributed among virtual servers rather than sitting idle waiting for load.
Virtualization is not limited to servers. Storage hypervisors use it for data storage. They run on physical hardware as VMs, within the system, or in another storage network. Hypervisors also help virtualize desktops and individual applications.
Virtualization began being used in the 1960s. For the most part, the virtualization environment was applied to IBM mainframes. Developers used it to test ideas and to study and refine hardware concepts. This made it possible to deploy systems and fix errors without threats to the stability of the primary equipment.
At the beginning of the new millennium, virtualization received a powerful boost thanks to widespread adoption in Unix family operating systems. There were several reasons for mass distribution:
This led to mass adoption. Since then, virtualization systems have been used not only for solving complex engineering tasks, but also for simple resource sharing and even home entertainment. In recent years, virtualization has expanded beyond x86 to ARM-based processors, with solutions like Apple's Virtualization framework and AWS Graviton instances becoming increasingly common.
Although virtual machines run on a single device, logical boundaries are built between them. This isolation protects against threats. If one virtual machine fails, others continue to operate.
Another huge advantage is mobility. VMs are independent of hardware. Want to migrate an environment to another server? No problem. Need to deploy a VM on a local computer? Also a simple task. Less connection to hardware means fewer dependencies.
Finally, resource savings. A hosting provider manages equipment more rationally by providing one physical server to multiple clients. Machines don't sit idle, but bring benefit with all their capabilities. Clients don't overpay for physical equipment while simultaneously gaining the ability to scale quickly and conveniently if such a need arises.
There are two types of hypervisors, concisely named Type 1 and Type 2.
TYPE 1: bare-metal hypervisors. They run on the computer's hardware. From there, they manage the equipment and guest systems. This type of virtualization is offered by Xen, Microsoft Hyper-V, Oracle VM Server, and VMware ESXi. Modern cloud providers also use specialized Type 1 hypervisors like AWS Nitro and KVM-based solutions.
TYPE 2: hosted hypervisors. They operate within the system as regular programs. Virtual systems in this case appear in the main system as processes. Examples include VirtualBox, VMware Workstation, VMware Player, and Parallels Desktop.
To increase the stability, security, and performance of hypervisors, developers combine features of both types, creating hybrid solutions. They work both on "bare metal" and using the host's main system. Examples include recent versions of Xen and Hyper-V.
The boundaries between bare-metal and hosted hypervisors are gradually blurring. However, it's still possible to determine the type. Though there's usually no practical need for this.
Virtualization types are not the only difference. Hypervisors solve different tasks, have different hardware requirements, and have licensing peculiarities.
A free hypervisor for servers running Windows OS. Its features:
Hyper-V uses encryption to protect virtual machines and also allows reducing and expanding disk space. Among the disadvantages: there's no USB Redirection needed for connecting USB devices to virtual hosts. Instead, Discrete Device Assignment is used, which is not a complete replacement.
VMware is a virtualization technology created by the American company of the same name. It's used to organize virtual server operations. In 2024, Broadcom acquired VMware and introduced significant changes to licensing models and product portfolios, shifting focus toward larger enterprise customers.
Many know about ESXi, a hardware hypervisor built on a lightweight Linux kernel called VMkernel. It contains all the necessary virtualization tools.
A license must be purchased for each physical processor to operate. The amount of RAM and how many virtual machines you plan to run on your equipment doesn't matter. Note that under Broadcom's ownership, licensing models have evolved, with many standalone products being bundled into subscription packages.
VMware has free virtualization tools. However, their capabilities are insufficient for professional use. For example, the API works in read-only mode, and the number of vCPUs must not exceed eight. Additionally, there are no backup management tools.
The VMware Workstation hypervisor was created in 1999. Now it's a virtualization tool for x86-64 computers with Windows and Linux. The hypervisor supports over two hundred guest operating systems. VMware Hypervisor has a free version with reduced functionality, typically used for familiarization and testing. In 2024, Broadcom made VMware Workstation Pro free for personal use, making it more accessible to individual users and developers.
An open-source tool designed for Linux/x86-based servers. Intel-VT and AMD-V extensions are also supported, and ARM virtualization extensions are increasingly common.
The KVM hypervisor is quite popular. It's used in many network projects: financial services, transportation systems, and even in the government sector. KVM is integrated into the Linux kernel, so it runs quickly. Major cloud providers use KVM as the foundation for their virtualization infrastructure. However, some disadvantages remain.
Built-in services are not comparable in functionality to other hypervisors' solutions. To add capabilities, third-party solutions must be used, such as SolusVM or more modern management platforms like Proxmox VE.
KVM is being refined by a community of independent developers, so gradually there are fewer shortcomings in its operation. The quality of the hypervisor is confirmed by hosting providers who choose it for virtualization on their equipment.
Xen is a cross-platform hypervisor solution that supports hardware virtualization and paravirtualization. It features minimal code volume. Modules are used to expand functionality. Open source code allows any specialist to modify Xen for their needs.
Oracle VM VirtualBox is a cross-platform hypervisor for Windows, Linux, macOS, and other systems.
It is one of the most popular hypervisors, especially in the mass market segment. This is partly because VM VirtualBox has open source code. The program is distributed under the GNU GPL license.
A distinctive feature: VirtualBox offers broad compatibility across different host and guest operating system combinations, making it ideal for development and testing environments.
Hypervisors are often contrasted with containers. They allow deploying a greater number of applications on a single device.
You already know what a hypervisor is and how it works. The problem is that VMs consume many resources. To operate, you need to make a copy of the operating system, plus a complete copy of the equipment for this system to function. If you allocate a nominal 4 GB of RAM to a VM, then the main device will have 4 GB less RAM.
Unlike VMs, a container only uses the operating system's resources. It also needs power to run a specific application. But much less is required than to run an entire OS.
However, containers cannot completely replace VMs. This is partly due to the increased risk of losing all data. Containers are located inside the operating system. If the host is attacked, all containers can be damaged or lost.
A virtualization server creates multiple virtual machines. They don't interact with each other; there are clear boundaries between them. If one machine is attacked, the others remain safe. Along with all their contents.
In modern infrastructure, containers and VMs are often used together. Container orchestration platforms like Kubernetes typically run on virtual machines, combining the isolation benefits of VMs with the efficiency of containers. This hybrid approach has become the standard for cloud-native applications.
Hypervisors are more secure than containers. However, they still have problems. Theoretically, it's possible to create a rootkit and malicious application that installs itself disguised as a hypervisor.
Such a hack is called hyperjacking. It's difficult to detect. Protection doesn't trigger because the malicious software is already installed and intercepts system actions. The system continues to work, and the user doesn't even suspect there are problems.
To protect the system from rootkits, specialists are developing various approaches that protect it without negatively affecting performance. Modern processors include hardware-based security features like Intel TXT and AMD Secure Encrypted Virtualization to help prevent hypervisor-level attacks.
The choice is vast: VMware or VirtualBox, Hyper-V or KVM. There's one universal recommendation: focus on the tasks. If you need to test an operating system in a virtual machine on a home computer, VirtualBox will suffice. If you're looking for a solution to organize a corporate-level server network, then the focus shifts toward VMware tools (keeping in mind recent licensing changes), KVM-based solutions like Proxmox, or cloud-native options.
For cloud deployments, consider managed hypervisor solutions from providers like Hostman, AWS, Azure, or Google Cloud, which abstract away much of the complexity while providing enterprise-grade performance and security.