Discuss the different types of hypervisors.


  • A hypervisor (also known as a virtual machine monitor, VMM, or virtualizer) is a type of computer software, firmware or hardware that creates and runs virtual machines. A computer on which a hypervisor runs one or more virtual machines is called a host machine, and each virtual machine is called a guest machine. The hypervisor presents the guest operating systems with a virtual operating platform and manages the execution of the guest operating systems. 
  • The term hypervisor is a variant of supervisor, a traditional term for the kernel of an operating system: the hypervisor is the supervisor of the supervisors, with hyper- used as a stronger variant of super.
  • A hypervisor is a function that abstracts, or separates, operating systems and applications from the underlying computer hardware. This abstraction enables the underlying host machine hardware to run one or more virtual machines as guests independently, allowing numerous guest VMs to effectively share the system's physical computational resources like processor cycles, memory space, network bandwidth, and so on. A hypervisor is also known as a virtual machine monitor.
  • A hypervisor, often known as a VMM (Virtual Machine Monitor), is a software layer that sits between the operating system and the hardware. It provides the services and functionality required for the seamless operation of several operating systems. It detects traps, reacts to privileged CPU instructions, and manages hardware request queuing, dispatching, and return. To administer and control the virtual machines, a host operating system runs on top of the hypervisor.
  • Hypervisors offer various advantages to the business data center. First, the capacity of a physical host system to operate numerous guest VMs may dramatically enhance resource usage. Whereas physical (non-virtualized) servers may only host one operating system and application, a hypervisor virtualizes the server, allowing the system to host multiple VM instances, each running an independent operating system and application, on the same physical system while utilizing far more of the system's available compute resources.
  • The abstraction that occurs in a hypervisor also allows the VM to be independent of the underlying hardware. Traditional software is often tightly connected to the underlying server hardware, which means that relocating the application to a different server necessitates time-consuming and error-prone reinstallation and customization. A hypervisor, on the other hand, renders the underlying hardware specifics irrelevant to the VMs. This enables VMs to be transferred or migrated between any local or distant virtualized servers with appropriate computational capacity nearly at a whim, with virtually no disturbance to the VM; a capability known as live migration.
  • Using hypervisor-based virtualization software to provide isolation between different customer environments can lead to increased utilization of system resources such as CPU and memory. Using native virtualization technologies offered by hardware vendors, such as Solaris Zones when using the Oracle Solaris operating system, can be much more effective and efficient depending on the customer environment. Native virtualization technologies offered by hardware vendors are more restrictive in terms of what is supported than hypervisor-based virtualization software.

Hypervisors are classified into two types: TYPE 1 and TYPE 2

Type 1 Hypervisor/native or bare-metal hypervisors

  • Type 1 hypervisors are those that operate directly on the system hardware. In vendor literature, they are frequently referred to as "native," "bare metal," or "embedded" hypervisors. Type 1 hypervisors are becoming more prevalent these days because incorporating the hypervisor into the firmware is more efficient. Type 1 hypervisors, according to IBM, provide better performance, availability, and security than Type 2 supervisors.
  • These hypervisors run directly on the host's hardware to control the hardware and manage guest operating systems. For this reason, they are sometimes called bare-metal hypervisors. The first hypervisors, which IBM developed in the 1960s, were native hypervisors. These included the test software SIMMON and the CP/CMS operating system, the predecessor of IBM z/VM.

Examples of Type 1 Hypervisor

1. VMware ESX and ESXi: These hypervisors provide extensive functionality and scalability, but they need a license, which raises the expenses. VMware provides certain low-cost bundles that might make hypervisor technology more economical for small infrastructures. VMware is the market leader in Type-1 hypervisors. Their vSphere/ESXi product is offered in five commercial variants as well as a free edition. 
2. Microsoft Hyper-V: The Microsoft hypervisor, Hyper-V, lacks many of the sophisticated 2.
capabilities are seen in VMware's solutions. Hyper-V, along with XenServer and vSphere, is one of the top three Type-1 hypervisors.
3. Citrix XenServer: It started as an open-source project. The underlying hypervisor technology is free but it lacks advanced functionality, much to VMware's free ESXi. Xen is a bare-metal hypervisor of type 1. Just as Red Hat Enterprise Virtualization uses KVM, Citrix uses Xen in the commercial XenServer.
4. Oracle VM: The Oracle hypervisor is built on the open-source Xen platform. However, if you require hypervisor support or product upgrades, you will be charged. Many of the sophisticated functionality present in competing for bare-metal virtualization hypervisors are missing from Oracle VM.

Type 2 Hypervisor / hosted hypervisors

  •  A host operating system is used by type 2 hypervisors. Type 2 hypervisors were the most popular when the virtualization trend initially took off. Administrators may purchase the program and install it on an existing server. IBM advises that Type 2 hypervisors be used primarily on client systems where efficiency is not as important, or on systems where support for a wide range of I/O devices is required and may be supplied by the host operating system.
  • These hypervisors run on a conventional operating system (OS) just as other computer programs do. A virtual machine monitor runs as a process on the host. Type-2 hypervisors abstract guest operating systems from the host operating system.
  • The distinction between these two types is not always clear. For instance, KVM and bhyve are kernel modules that effectively convert the host operating system to a type-1 hypervisor.[7] At the same time, since Linux distributions and FreeBSD are still general-purpose operating systems, with applications competing with each other for VM resources, KVM and bhyve can also be categorized as type-2 hypervisors.

Examples Of Type 2 Hypervisor 

1. VMware Workstation/Fusion/Player: VMware Player is a virtualization hypervisor that is available for free. It is designed to operate only one virtual machine (VM) and does not support the creation of new VMs. VMware Workstation is a more powerful hypervisor that includes sophisticated capabilities like record-and-replay and VM snapshot support.

2. VMware Workstation offers three key use cases: running various operating systems or versions of one operating system on a single desktop, for developers who require sandbox environments and snapshots, and for laboratories and demonstration purposes.

3. VMware Server: VMware Server is a free, hosted virtualization hypervisor that functions similarly to VMware Workstation.

 4. Microsoft Virtual PC: Windows Virtual PC is the most recent virtualization technology from Microsoft. It enables you to run a wide range of productivity programs in a virtual Windows environment with a single click, directly from a Windows 7-based PC. 

5. Oracle VM VirtualBox: If you wish to virtualize on a budget, VirtualBox hypervisor technology delivers enough performance and functionality. Although it is a free, hosted solution with a tiny footprint, VirtualBox has several features in common with VMware vSphere and Microsoft Hyper-V. 

6. Red Hat Enterprise Virtualization: Red Hat's Kernel-based Virtual Machine (KVM) combines the advantages of a hosted and bare-metal virtualization hypervisor. It is capable of converting the Linux kernel into a hypervisor, allowing VMs direct access to physical hardware.


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