What is a hypervisor in virtualization?

A hypervisor, also known as a virtual machine monitor (VMM), is a piece of computer software, firmware or hardware that creates and runs virtual machines. A hypervisor allows multiple operating systems to share a single hardware host.

What is a hypervisor in virtualization?

How does a hypervisor work?

A hypervisor creates a layer between the hardware and the virtual machines, controlling and allocating computer resources to the virtual machines. The hypervisor itself runs directly on the server hardware, while the virtual machines run as guest operating systems on top of the hypervisor.

When a virtual machine makes a request for resources, the hypervisor translates this request and allocates resources accordingly from the physical hardware. The hypervisor then allows the virtual machines to share resources like CPU, memory, storage and network bandwidth from the host computer.

Key responsibilities of a hypervisor include:

  • Virtualizing and sharing physical resources between virtual machines
  • Enforcing isolation between virtualized environments
  • Managing communications between virtual machines
  • Allocating hardware resources to meet changing workloads

Types of hypervisors

There are two main types of hypervisors:

Type 1 hypervisors

Type 1 hypervisors, also known as bare-metal or native hypervisors, run directly on the system hardware. The hypervisor interacts with the hardware directly rather than through an intervening operating system.

Examples of Type 1 hypervisors include:

  • VMware vSphere ESXi
  • Microsoft Hyper-V
  • Citrix XenServer


  • Better performance and efficiency
  • Greater stability and security
  • Allows for more virtual machines per host

Type 2 hypervisors

Type 2 hypervisors run as software applications on an operating system, like other computer programs. The operating system is referred to as the “host machine” and the virtual machines created and managed by the hypervisor run as “guest machines” on the host.

Examples of Type 2 hypervisors include:

  • VMware Workstation
  • Oracle VirtualBox
  • Parallels Desktop


  • Easier to install as an application on an existing OS
  • Allows leverage of host OS drivers and libraries
  • Portable between similar host OS instances

What are the key functions of a hypervisor?

Fundamentally, hypervisors allow hardware virtualization – creating virtual versions of computing resources like CPU, memory and storage. This allows multiple operating systems to run concurrently on a single physical machine.

Key functions include:

Partitioning hardware resources

The hypervisor partitions the underlying server hardware resources into isolated execution environments called virtual machines (VMs). Resources like CPU processing, RAM memory and storage capacity are divided and dedicated to distinct VMs.

Facilitating inter-VM communications

The hypervisor facilitates communications such as networking between virtualized environments while maintaining isolation between them. This allows connected VMs to communicate while data and processes are kept segmented.

Virtualizing physical system resources

The hypervisor presents a virtual operating platform to each guest machine. It emulates hardware like CPU instruction sets, memory space, hard disk storage, ACPI power features and input/output devices to create virtual equivalents.

Managing resource allocation

As workloads change in real-time, the hypervisor schedules timing access across VMs to adaptively balance workloads. This “shares” physical resources dynamically between VMs as needed.

Enabling live migration of VMs

Hypervisors support live migration of active virtual machines between host servers to enable fault tolerance and load balancing across infrastructure.

Monitoring and optimizing performance

Hypervisors expose metrics for fine-grained monitoring of system utilization metrics to enable optimization of configurations for performance and efficiency.

Key benefits of hypervisors

Hypervisors and hardware virtualization deliver major technology and business benefits:

Increased hardware efficiency

By allowing workloads to share hardware resources, utilization rates of physical servers can be increased dramatically. More workloads can be deployed on existing infrastructure.

Improved business continuity

VMs can be live migrated between hosts to keep business-critical applications running smoothly in case of planned or unplanned downtime events.

Cross-platform support

Hypervisors allow hardware to run diverse OS environments like Windows, Linux and custom appliances on a common infrastructure platform.

Faster provisioning

New servers and workloads can be provisioned as software-defined VMs that starts instantly – dramatically faster than procuring and configuring new physical servers.

Better workload isolation

Performance-critical applications can be isolated from noisy neighbor issues on multi-tenant infrastructure for more consistent performance.

Increased test agility

Development and QA teams can provision finely tuned test environments in software as needed for more flexible testing.

Enhanced disaster recovery

Backups of entire virtual environments ease disaster recovery processes. VMs can start up instantly on spare capacity or in the cloud.

Challenges with hypervisors

While virtualization delivers immense value, hypervisors also introduce challenges around management complexity and performance:

  • Increased operational overhead – Being software-defined infrastructure, hypervisor hosts require careful monitoring, optimization and systems management.
  • Learning curve – IT talent may lack skills in this technology, requiring training investments around virtualization.
  • Potential performance issues – Compared to native hardware, hypervisor abstractions impose slight latencies that can impact application performance if systems are not properly configured.
  • Live migration dependencies – Seamless live migration relies on shared storage across infrastructure, which adds cost and complexity.
  • Security considerations – Consolidating applications on shared infrastructure increases attack surfaces. Locking down hypervisor access control and patch management is critical.

Hypervisor virtualization use cases

Major environments where hardware virtualization is commonly used:

Server consolidation

Hypervisors allow companies drastic reductions in physical servers, saving enormously on capital and operating costs. Server footprints can often be reduced 10:1 or greater.

Cloud computing infrastructure

Public cloud platforms like AWS EC2, Azure Virtual Machines, and private clouds intrinsically utilize hypervisors to enable flexible provisioning of customer VMs on shared infrastructure.

Application isolation

Hypervisors provide strong separation between applications, guarding against configuration issues impacting adjacent workloads. This facilitates stability and security.

Development, testing and staging

Hypervisor tools like VMware Workstation enable programmers to replicate and sandbox production environments for application development and testing.

Disaster recovery

Backups of virtual environments allow instant failover to standby systems locally or in cloud sites in case primary sites go offline due to natural disasters or technical problems.

Virtual desktops

Solutions like VMware Horizon provision thousands of persistent or non-persistent virtual desktops to enable secure access and simplified management.

Hypervisor vendors

Leading hypervisor platform vendors include:

  • VMware – Founded the x86 virtualization market with VMware ESXi and vSphere. Offers industry-leading capabilities for data centers, clouds and end user computing.
  • Microsoft – Hyper-V ships free with Windows Server, leveraging tight Windows support for common management and guest OS hosting.
  • Linux KVM – The Kernel-based VM integrated into the Linux kernel is open source and powers major public cloud platforms.
  • Citrix – Citrix XenServer targets hosting Linux, Windows, BSD and other OS environments with strong management tools.
  • Oracle – The Oracle VM Server for x86 focuses performance optimizations on hosting Oracle database and application workloads.

Key Takeaway

  • A hypervisor, also called a virtual machine monitor (VMM), creates and runs virtual machines on underlying server hardware.
  • By creating abstractions of physical resources, hypervisors enable multiple workloads and operating systems to efficiently share resources on the same infrastructure. This enables significant operational, financial and technology benefits.
  • Leading hypervisor platforms help organizations consolidate and modernize infrastructure, facilitate secure application development, enable more robust business continuity protections and transition workloads to the cloud.


In closing, hypervisors deliver immense value as foundational platforms for hardware virtualization. By dividing physical infrastructure into isolated virtual machines, hypervisors transform how companies utilize data center resources. With capabilities spanning server consolidation, cross-platform support, workload migration and cloud infrastructure, leading hypervisor solutions like VMware vSphere, Microsoft Hyper-V, Linux KVM and Citrix provide technologies central to the modern software-defined data center.


  1. What is the difference between Type 1 and Type 2 hypervisors?
    Type 1 hypervisors run directly on server hardware, while Type 2 hypervisors run as software applications on host operating systems. Type 1 hypervisors offer better performance while Type 2 hypervisors are easier to install.
  2. How does a hypervisor enable virtual machines?
    By partitioning and virtualizing physical resources like CPU, memory and storage, hypervisors present a virtual hardware environment to each virtual machine. This facilitates the concurrent hosting of multiple operating systems.
  3. What capabilities do hypervisors provide?
    Key capabilities include partitioning of hardware resources, facilitating VM networking, providing virtual hardware abstractions, adaptive resource scheduling, live migration of VMs and performance monitoring.
  4. What are the benefits of virtualization with hypervisors?
    Major benefits include increased infrastructure efficiency, improved business continuity, faster application provisioning, enhanced workload isolation, easier disaster recovery and cross-platform operating system support.
  5. What are the main uses of hypervisor virtualization?
    Leading use cases include server consolidation, powering cloud computing infrastructure, isolating applications, accelerating software development and testing, enabling virtual desktops and facilitating disaster recovery configurations.
  6. Who are the major hypervisor vendors?
    The major hypervisor platform vendors are VMware, Microsoft, Linux KVM, Citrix and Oracle. VMware ESXi, Microsoft Hyper-V and Linux KVM dominate across cloud and enterprise installations.
  7. How do hypervisors improve hardware utilization efficiency?
    By enabling multiple virtual machines to share physical resource pools, hypervisors raise utilization levels – allowing more workloads to be deployed on existing infrastructure. This increases efficiency and saves on hardware costs.
  8. How do hypervisors help with business continuity?
    Live migration of VMs enables dynamic failover to backup systems locally or in cloud sites, keeping mission-critical applications running through planned and unplanned outages.
  9. How does virtualization simplify cross-platform operating system support?
    With hypervisor-mediated hardware virtualization, organizations can readily host heterogeneous workloads spanning Windows, Linux, BSD and custom virtual appliances across standardized infrastructure.
  10. How do hypervisors accelerate application provisioning times?
    Rather than needing to procure and configure new physical servers which can take weeks or longer, new servers can be provisioned as instantly available VMs on existing hypervisor infrastructure.
  11. How can hypervisors improve workload isolation and consistency?
    By partitioning hardware into isolated VMs, hypervisors insulate applications from the impacts of noisy neighbors on shared infrastructure which helps improve performance stability.
  12. How do hypervisors ease disaster recovery processes?
    Backups of full virtual machine environments allow failed over workloads to start instantly on spare capacity or standby sites, minimizing downtime. No physical-to-physical recovery is required.

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