What are hypervisors? – IBM

VMware Hypervisors

Offers Hypervisors


1 and Type 2. Type 1 hypervisors include:

  • ESXi hypervisor. VMware ESXi (Elastic Sky X Integrated) is a Type 1 (or bare metal) hypervisor for server virtualization in the data center. ESXi manages collections of VMware virtual machines.
  • VSphere hypervisor. Customers can use VMware ESXi for free as part of the free vSphere hypervisor, which is a basic server virtualization offering. Enterprises with enterprise cloud environments will license vSphere, a more comprehensive system that includes a license for VMware’s vCenter Server. This is a stand-alone server that is used to manage vSphere environments running on physical hosts. VSphere can run in a private cloud environment or in a hosted cloud configuration.


also offers Type 2 hypervisor products

for desktop and laptop users: VMware Fusion: This is the

  • company’s MacOS-centric offering, which allows Mac users to run a wide range of guest operating systems
  • .

  • Workstation: VMware’s Linux- and Windows-centric platform comes in two flavors: Pro, which is a paid version, and Player, which is free for personal use. The Pro version allows users to run multiple operating systems on a single PC and also connects to VMware vSphere, just like Fusion. Workstation Player only supports a single guest operating system.
  • VirtualBox: A Type 2 hypervisor that runs on Linux, Mac OS, and Windows operating systems. Oracle inherited the product when it bought Sun Microsystems in 2010.

Hyper-V Hyper-V Hypervisor

is Microsoft’s hypervisor designed for use on Windows systems. It was released in 2008 as part of Windows Server, meaning customers needed to install the entire Windows operating system to use it. Subsequently, Microsoft made available a dedicated version called Hyper-V Server, which ran on Windows Server Core. This allowed administrators to run Hyper-V without installing the full version of Windows Server. Hyper-V is also available on Windows clients.

Microsoft designates Hyper-V as a Type 1 hypervisor, even though it runs differently than many competitors. Hyper-V is installed on Windows, but runs directly on the physical hardware, inserting itself underneath the host operating system. All guest operating systems run through the hypervisor, but the host operating system gets special access to the hardware, giving it a performance advantage.



XenServer, now known as Citrix Hypervisor, is a commercial Type 1 hypervisor that supports both Linux and Windows operating systems. XenServer was born from the Xen open source project (link resides outside ibm.com).




such as KVM, come from open source projects. Red Hat’s ties to the open source community have made KVM the core of all major OpenStack and Linux virtualization distributions.

Open source hypervisors are also available in free configurations. KVM can be downloaded alone or as part of the oVirt open source virtualization solution, of which Red Hat is a long-term supporter.

Another is Xen, which is a Type 1 open source hypervisor that runs on Intel and ARM architectures. It started as a project at Cambridge University and his team later commercialized it by founding XenSource, which Citrix bought in 2007.

In 2013, the open source project became a collaborative project under the Linux Foundation. Many cloud service providers use Xen to power their product offerings.

Xen supports several types of virtualization, including hardware-assisted environments using Intel VT and AMD-V. It also supports paravirtualization, which tunes the guest operating system to work with a hypervisor, delivering performance gains.

Hypervisor KVM

Linux also has hypervisor capabilities built directly into your operating system kernel. The kernel-based virtual machine (KVM) became part of the mainline Linux kernel in 2007 and complements QEMU, which is a hypervisor that emulates the physical machine’s processor entirely in software.

KVM supports virtualization extensions that Intel and AMD built into their processor architectures to better support hypervisors. These extensions, called Intel VT and AMD-V respectively, allow the processor to help the hypervisor manage multiple virtual machines. When these extensions are available, the Linux kernel can use KVM. Otherwise, go back to QEMU.

Learn more about KVM (link resides outside ibm.com) at Red Hat.

Red Hat hypervisor

Red Hat

bases its Red Hat Enterprise Virtualization Hypervisor on the KVM hypervisor. Your virtualization solution creates additional installations around the hypervisor. This includes a virtualization manager that provides a centralized management system with a search-based graphical user interface and secure virtualization technologies that harden the hypervisor against attacks targeting the host or virtual machines. Red Hat’s hypervisor can run many operating systems, including Ubuntu.

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