What Is a Hypervisor? Definition, Types, and Software

A hypervisor is defined as hardware, software, or firmware for creating and operating virtual machines (VM). Also known as a virtual machine monitor (VMM), the hypervisor runs on a host machine and allows it to support multiple guest VMs through virtual resource sharing. This article covers the definition and types of hypervisors and the top software in the hypervisor space.

What Is a Hypervisor?

A hypervisor is a hardware, software, or firmware for creating and operating virtual machines (VM). Also known as a virtual machine monitor (VMM), the hypervisor runs on a host machine and allows it to support multiple guest VMs through virtual resource sharing.

Hypervisors enable users to create and manage VMs by abstracting software from hardware. Virtualization takes place through the translation of requests between hardware and virtual resources. Native hypervisors can even be embedded into the firmware at the motherboard BIOS level, allowing the computer’s operating system to leverage virtualization software.

Why use a hypervisor?

Hypervisors allow the system to utilize its available resources better and enhance IT mobility by helping guest VMs operate independently from the host hardware. This gives users the power to transfer VMs easily between servers. A hypervisor gives a single physical server the ability to run multiple virtual machines, thus reducing the requirement for space, maintenance, and motive power.

Apart from this, hypervisors enhance operational speed when it comes to VMs. Users can instantly create VMs through streamlined resource provision as per dynamic workload requirements.

Enhanced efficiency is another benefit of using a hypervisor. A virtual machine monitor can run numerous VMs on the resources of one physical machine, thus facilitating efficient server utilization. This improves the cost and energy efficiency of VM operations, helping establish a more viable process than deploying multiple underutilized physical machines.

Using bare-metal hypervisors makes operating systems and applications compatible with different hardware types. This is achieved by separating the operating system from the underlying physical machine. Essentially, the hypervisor removes the software’s reliance on specific drivers or devices.

Portability is another crucial reason for the use of hypervisors. Virtual machine monitors enable numerous operating systems to be hosted on the same server, which serves as the host machine. The VMs managed using the hypervisor are portable since they are decoupled from the hardware.

Finally, with a hypervisor, IT workloads can be shifted as desired among servers. Resource allocation for networking, storage, processing, and memory is streamlined across servers, machines, and platforms. For instance, if an application on one virtual machine requires greater processing power, it uses the virtualization software powered by the hypervisor to access the unused resources of other devices.

Hypervisor vs. container

Both containers and hypervisors boost application speed and efficiency. However, they achieve their goals differently and are used for different purposes.

See More: What Is Software as a Service (SaaS)? Definition, Examples, Types, and Trends

Types of Hypervisors

Two main types of hypervisors are used based on their location in the server virtualization structure.

1. Type 1 hypervisor

A type 1 hypervisor, also called a native or bare-metal hypervisor, is a software layer directly installed on a physical server’s underlying hardware. The term ‘bare-metal’ is used because no other software runs between the hypervisor and the hardware. This hypervisor type is commonly seen in enterprise use.

Type 1 hypervisors do not need a third-party operating system to run. Instead, they use a barebones operating system specialized for running virtual machines. This helps enhance their stability and performance. The host machine with a type 1 hypervisor is dedicated to virtualization. When a server with a native hypervisor installed boots up, it displays a prompt with network and hardware details such as CPU, memory, MAC address, and IP address.

Advantages of type 1 hypervisors

The key benefits of bare-metal hypervisors include improved security and performance.

• Improves cybersecurity: Native hypervisors feature a direct connection to hardware without needing an extra operating system layer. This integrated access significantly reduces the attack surface that malicious actors can target.
• Enables VM mobility: A bare-metal hypervisor allows users to transfer VMs automatically or manually between physical servers. Mobility is based on the dynamic resource requirements of virtual machines and does not negatively impact end-users; in fact, they are often unaware of the changes in the VM location as it is a seamless process. 

This feature is also useful in case of hardware failure–the virtual machine management software simply transfers all VMs away from the failed server and onto a working server. Detection and restoration are carried out automatically as well.

• Supports resource overallocation: Type 1 hypervisors allow users to assign ‘more than available’ resources to virtual machines. For instance, if a server comes equipped with 256 gigabytes of RAM and is loaded with six virtual machines, each VM can be assigned 48 gigabytes of RAM. This totals 288 gigabytes of RAM; however, the VMs will not continuously consume their allocated 48 gigabytes from the server hardware. 

Rather, the hypervisor will allocate RAM to the VMs as per their resource requirements, and they will use the quantity of RAM that they need to execute specific tasks. One reason present-day enterprise data centers leverage type 1 hypervisors is the allocation of resources required for the instance’s complete functionality.

Disadvantages of type 1 hypervisors

Complexity and limited capability for advanced management are the two key disadvantages of type 1 hypervisors.

• Complex management: Creating virtual instances with a native hypervisor requires users to set up a management console on a separate computer. The console connects to the hypervisor installed on the server and can then be used to manage the virtual environment.
• Constraints on functionality: Type 1 hypervisors lack certain features and are relatively simple in terms of functionality. Their key operations include changing the time, date, password, IP address, etc.
• Price variability: The licensing price for management consoles depends on the functionalities needed and can vary considerably.

2. Type 2 hypervisor

A type 2 hypervisor, also called a hosted hypervisor, is ‘hosted’ within the third-party operating system of a physical server–thus its name. Unlike native hypervisors that operate directly on the underlying server hardware, type 2 hypervisors have a single software layer– the operating system – between them and the physical hardware.

The general components of a hosted hypervisor include physical hardware; an operating system such as Windows, macOS, or Linux operating on the hardware; a hosted hypervisor software installed on top of the operating system; and the virtual guest instances. Such hypervisors are normally found in environments with fewer servers.

All type 2 hypervisor operations take place on the server equipped with the hypervisor. A management console installed on a separate system is not required for managing VMs in this hypervisor type because the hosted hypervisor performs the VM management console’s duties. VMs are launched within the regular windows of the operating system, and all tasks are executed through in-built functionalities.

Advantages of type 2 hypervisors

Hosted hypervisors are easy to use and have significant productivity benefits.

• Compatibility with more applications: Type 2 hypervisors offer users compatibility with applications that are available for their primary operating system and those for other operating systems. For instance, a macOS user can access applications for Windows by creating a Windows VM.
• Easy management: A separate management console software does not need to be installed on a different machine to create and maintain the virtual environment. Users simply need to install and operate the type 2 hypervisor software like any other application within their primary operating system. Users can also seamlessly create snapshots, clone VMs, import and export appliances, and execute other VM management tasks.
• Suitable for testing: Most users prefer type 2 hypervisors for their convenience during software testing. This is because hosted hypervisors can run multiple virtual instances of various operating systems and configurations on a single physical machine. This allows for the testing of application behavior in different environments, as well as the creation of network environments with varying specifications. The only requirement from the user’s side is ensuring sufficient physical resources for the operation of the host and all virtual machines.

Disadvantages of type 2 hypervisors

Compared to bare-metal hypervisors, hosted hypervisors can be less secure and have constraints on performance.

• Inflexible resource allocation: Allocating resources on a hosted hypervisor is less flexible than doing so with a native hypervisor. Type 1 hypervisors can dynamically allocate available computing resources according to the real-time needs of specific VMs. On the other hand, type 2 hypervisors can only access whatever resources are allocated by the user to specific VMs. For instance, if 8 gigabytes of RAM are assigned to a VM, that RAM is ‘earmarked’ by the VM, even if only a fraction of it is used. The host computer cannot access resources allocated to a virtual machine while that VM operates.
• Performance constraints: With the host and guest operating systems concurrently using the host machine’s resources, additional performance pressure is placed on the physical hardware. This can lead to latency issues within the guest VMs.
• Wider attack surface: Hosted hypervisors are installed and operate on top of the native operating system of the host machine. This presents potential cybersecurity risks, as attackers can target the vulnerabilities of the primary operating system or the applications on it to access the virtual instances.

Choosing the right hypervisor type

No objectively right hypervisor type exists; it all depends on the individual needs of the deployment.

Begin by accounting for the planned size of the virtual environment that is to be deployed. Personal or smaller enterprise deployments will find type 2 hypervisors more convenient. Large-scale enterprise environments generally thrive with type 1 hypervisors; however, one must consider licensing costs before making a decision.

Licensing can be priced on a per CPU, per server, or per core basis. Leading vendors cater to numerous enterprise deployment types with multiple product types and licensing layers. A good way to get the best deal is to involve all stakeholders in creating a comprehensive list of the requirements for the virtual enterprise environment. This list can help enterprise decision-makers, perhaps in collaboration with the vendor, decide features such as the number of VMs required, resources allocated to each VM, particular functionalities, and nodes per cluster.

What is a cloud hypervisor?

Today, cloud computing is present in some form or the other in almost every tech-enabled enterprise. The hypervisor is emerging as a useful tool for managing VMs in the cloud. A hypervisor essentially serves as a software layer for a single host computer to concurrently manage numerous VMs–a concept that can be extended to the cloud as well.

Cloud hypervisors are deployed to make cloud-powered applications available to end users across virtual environments without IT teams having to compromise on control over the cloud infrastructure and data. One reason for the growing popularity of cloud hypervisors is the impetus for digital transformation at the org level. This, in turn, is driven by increasing customer expectations and the clear need for innovation to stay ahead of the competition. As enterprises migrate virtual environments to the cloud, cloud hypervisors will continue to see substantial demand growth.

Hypervisors also play a role in virtualizing applications for quicker migration to the cloud. Enterprises are relying on the virtualization capabilities of hypervisors to access the many benefits of cloud computing, including enhanced accessibility, increased scalability, minimized hardware expenditures, and greater returns on investment.

Finally, cloud hypervisors are a useful tool for rewriting existing applications for the cloud, minimizing the consumption of IT resources, and demolishing infrastructure silos in the process.

See More: What Is Middleware? Definition, Architecture and Best Practices

Top 9 Hypervisor Software

Numerous leading vendors operate in the hypervisor software space. Most hypervisor providers offer trial periods or low-feature free software versions to enable users to test their products before buying them.

Let’s look at the top hypervisor software from leading vendors:

1. VMware vSphere

VMware is an industry leader in virtualization technology. It provides vSphere and numerous other virtualization solutions to several large-scale data centers.

VMware vSphere is a type 1 hypervisor with several advanced features and commercial editions. A free version of this hypervisor exists as well. The licensing fees of this solution can prove to be on the higher side, making it less ideal for smaller virtual environments.

2. Oracle VM VirtualBox

VirtualBox is a stable-hosted hypervisor solution distributed free of cost by Oracle. It comes with sufficient features for advanced personal use and is capable of fulfilling most use cases for smaller enterprises as well.

Oracle VM VirtualBox is not resource-intensive and is well-suited for desktop and server virtualization. It can support guest multiprocessing with up to 32 vCPUs per VM, snapshot trees, PXE Network boot, and many other useful features.

3. Microsoft Hyper-V

Microsoft’s Hyper-V is a native hypervisor solution that has proven to be a worthwhile substitute for VMware. While a free edition of this hypervisor solution exists, it lacks the GUI and many useful features that are bundled with the commercial versions. Its key functionalities include live migration, VM replication, and dynamic memory.

4. Parallels Desktop

This type 2 hypervisor solution is a viable alternative for VMware Fusion. Primarily targeted to macOS users, it offers numerous features based on the version purchased. Key features include network conditioning, Docker integration, 128 gigabytes of support for each VM, and compatibility with Chef, Ohai, and Vagrant.

5. VMware Workstation Pro and VMware Fusion

VMware Workstation Pro is a type 2 hypervisor compatible with Windows and Linux. It comes with several advanced features, including seamless vSphere integration. Workstation Pro allows users to transfer applications between desktop and cloud environments without hassle.

No free version of this solution exists yet, although users who wish to test hypervisors hosted by VMware can try VMware Workstation Player at no cost. Workstation Player is a feature-light version of the Workstation Pro hypervisor created for smaller sandbox-style virtual environments.

VMware Fusion is a hypervisor solution similar to Workstation Pro but created for macOS users. While its features are fewer, its price tag is smaller too.

6. Kernel-Based Virtual Machine

Commonly known as KVM, this bare-metal hypervisor solution is built into Linux and allows users to transform the kernel into a hypervisor. While some users believe that KVM should be classified as a type 2 hypervisor, you should note that this solution has direct hardware access that it passes along to its hosted VMs.

This open-source hypervisor solution comes with all Linux features and additional functions. It is a leading choice for enterprise deployments. Salient features include scheduling and resource control, higher prioritization, and live migration.

7. Citrix Hypervisor

Formerly known as Xen Server, this server virtualization solution is a native hypervisor well-suited for enterprise use. Citrix Hypervisor can process numerous workload types, and its features support the completion of demanding virtualization tasks. Proprietary features include Direct Inspect APIs for workload security and Intel- and NVIDIA-enhanced virtualized graphics.

8. Oracle VM Server for x86

This bare-metal hypervisor solution features the open-source Xen at its core. While the offering is free of cost, Oracle has announced the end of premier support as of March 2021 and has notified users that extended support will end by March 2024.

Oracle VM Server for x86 features an integrated web-based management console and supports Linux, Solaris, and Windows guests. It comes with a certified, fully-tested Oracle Applications stack in a virtualization environment for enterprise use.

9. Windows Virtual PC

Finally, this hosted hypervisor solution by Microsoft is only compatible with host machines running Windows 7. Guest machines can be loaded exclusively with Windows operating systems, including several versions of Windows 7, Vista, and XP SP3. This solution is completely free of cost.

See More: What Is Anything/Everything as a Service (XaaS)? Definition and Key Trends

Takeaway

A hypervisor is essential for server virtualization (simulation or emulation of physical resources through software). This solution is mainly used for creating and managing VMs using physical hardware resources.

The primary role of a hypervisor is to abstract and isolate virtual machines and the applications within them from underlying physical hardware. This helps ensure higher efficiency when it comes to using physical resources. Hypervisors also simplify management and maintenance, as well as minimize costs. Additionally, hypervisor-enabled server virtualization is practical when enabling cloud computing, giving rise to the demand for cloud hypervisors.

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