What is a Hypervisor? | VMware Glossary (2024)

There are several benefits to using a hypervisor that hosts multiple virtual machines:

• Speed:Hypervisors allow virtual machines to be created instantly, unlike bare-metal servers. This makes it easier to provision resources as needed for dynamic workloads.
• Efficiency:Hypervisors that run several virtual machines on one physical machine’s resources also allow for more efficient utilization of one physical server. It is more cost- and energy-efficient to run several virtual machines on one physical machine than to run multiple underutilized physical machines for the same task.
• Flexibility:Bare-metal hypervisors allow operating systems and their associated applications to run on a variety of hardware types because the hypervisor separates the OS from the underlying hardware, so the software no longer relies on specific hardware devices or drivers.
• Portability:Hypervisors allow multiple operating systems to reside on the same physical server (host machine). Because the virtual machines that the hypervisor runs are independent from the physical machine, they are portable. IT teams can shift workloads and allocate networking, memory, storage and processing resources across multiple servers as needed, moving from machine to machine or platform to platform. When an application needs more processing power, the virtualization software allows it to seamlessly access additional machines.
  

Hypervisors make it possible to use more of a system’s available resources and provide greater IT mobility since the guest VMs are independent of the host hardware. This means they can be easily moved between different servers. Because multiple virtual machines can run off of one physical server with a hypervisor, a hypervisor reduces:

• Space
• Energy
• Maintenance requirements
  

There are two main hypervisor types, referred to as “Type 1” (or “bare metal”) and “Type 2” (or “hosted”). Atype 1 hypervisoracts like a lightweight operating system and runs directly on the host’s hardware, while atype 2 hypervisorruns as a software layer on an operating system, like other computer programs.

The most commonly deployed type of hypervisor is the type 1 or bare-metal hypervisor, where virtualization software is installed directly on the hardware where the operating system is normally installed. Because bare-metal hypervisors are isolated from the attack-prone operating system, they are extremely secure. In addition, they generally perform better and more efficiently than hosted hypervisors. For these reasons, most enterprise companies choose bare-metal hypervisors fordata centercomputing needs.

While bare-metal hypervisors run directly on the computing hardware, hosted hypervisors run on top of the operating system (OS) of the host machine. Although hosted hypervisors run within the OS, additional (and different) operating systems can be installed on top of the hypervisor. The downside of hosted hypervisors is that latency is higher than bare-metal hypervisors. This is because communication between the hardware and the hypervisor must pass through the extra layer of the OS. Hosted hypervisors are sometimes known as client hypervisors because they are most often used with end users and software testing, where higher latency is less of a concern.

Hardware acceleration technology can create and manage virtual resources faster by boosting processing speed for both bare-metal and hosted hypervisors. A type of hardware accelerator known as avirtual Dedicated Graphics Accelerator(vDGA) takes care of sending and refreshing high-end 3-D graphics. This frees up the main system for other tasks and greatly increases the display speed of images. For industries such as oil and gas exploration, where there is a need to quickly visualize complex data, this technology can be very useful.

Both types of hypervisors can run multiple virtual servers for multiple tenants on one physical machine. Public cloud service providers lease server space on the different virtual servers to different companies. One server might host several virtual servers that are all running workloads for different companies. This type of resource sharing can result in a “noisy neighbor” effect, when one of the tenants runs a large workload that interferes with the server performance for other tenants. It also poses more of a security risk than using a dedicated bare-metal server.

A bare-metal server that a single company has full control over will always provide higher performance than a virtual server that is sharing a physical server’s bandwidth, memory and processing power with other virtual servers. The hardware for bare-metal servers can also be optimized to increase performance, which is not the case with shared public servers. Businesses that need to comply with regulations that require physical separation of resources will need to use their own bare-metal servers that do not share resources with other tenants.