What is a hypervisor in VMware?

A hypervisor, also known as a virtual machine monitor (VMM), is a layer of software, firmware or hardware that creates and runs virtual machines (VMs). A hypervisor allows multiple operating systems to share a single hardware host. Each virtual machine has its own set of virtual hardware resources allocated to it, but the hypervisor manages and arbitrates access to the actual physical hardware resources.

What is a hypervisor in VMware?

In VMware environments, the hypervisor is known as vSphere ESXi. It is the virtualization layer that manages compute, storage and networking resources to enable virtualization.

How a VMware hypervisor works

The role of the VMware vSphere ESXi hypervisor is to efficiently provide virtual resources to guest operating systems running in virtual machines. Here is a overview of how it works:

  • The hypervisor inserts itself between the server hardware and guest operating systems to allocate resources and allow for safe virtual machine isolation and security.
  • vSphere ESXi bare metal installs directly onto physical server hardware, allowing it to interact with the hardware at low levels not possible in hosted architectures.
  • When a guest OS makes a request for CPU, memory, storage or network resources, the hypervisor allocates what has been assigned to the virtual machine.
  • If needed, the hypervisor dynamically allocates additional resources if available based on policies.
  • Features like VMware vSphere vMotion allow for live migration of VMs between physical hosts to balance loads.
  • CPU and memory resources are allocated using scheduling algorithms and policies customized for particular types of workloads.

By efficiently sharing resources between virtual machines, the VMware hypervisor enables higher server hardware consolidation ratios and utilization.

Hypervisor architectural components

The vSphere ESXi hypervisor consists of these core components that enable virtualization:

VMkernel – This is a proprietary kernel and service layer that provides CPU and memory virtualization along with other critical services that enable the hypervisor to run and manage VMs.

Hardware abstraction layer – Sits between the VMkernel and physical server hardware to hide hardware differences allow virtual machines to have a consistent view of processor, memory and devices. It translates virtual resource requests to physical hardware calls.

Device drivers – Drivers to manage specific hardware resources including Ethernet NICs, Fibre Channel HBAs, SATA controllers and other devices making them available to virtual machines.

Management agents – These agents communicate with VMware vCenter Server as well as tools to monitor hypervisor health status and activity.

Bare metal vSphere ESXi hypervisor benefits

There are several key advantages to using vSphere ESXi’s bare metal hypervisor architecture compared to other hosted virtualization solutions:

Near-native performance – Since this Type 1 hypervisor runs directly on the server hardware, VMs get excellent compute, memory and I/O performance approaching that of non-virtualized environments.

Better security isolation – Running directly on the hardware enhances isolation between VMs and reduces the host OS attack surface that exists in Type 2 hypervisors running as an application.

Superior scalability – vSphere ESXi efficiently scales up to 64 physical host nodes allowing for thousands of VMs in a cluster as infrastructure demands grow.

Advanced features support – Type 1 hypervisors can take better advantage of modern hardware capabilities including paravirtualization for higher network, storage and video efficiency.

Greater stability – By not having to rely on a host operating system, potential application conflicts, library dependency issues and security patches don’t affect hypervisor patch schedules.

By leveraging vSphere ESXi’s tiny footprint and bare metal architecture, organizations can achieve simpler, more secure and massively scalable virtualized infrastructure.

VMware vSphere hypervisor editions

VMware packages several editions of its vSphere hypervisor to align with various business needs:

vSphere ESXi Free – Free edition ideal for smaller deployments. Limited to 8 physical CPU cores with basic management capabilities. No live migration of VMs between hosts.

vSphere ESXi Foundation – Low-cost starter solution removes some limits of the free version. Foundation license covers up to 2 physical processors with up to 2-WAY CPUs each.

vSphere ESXi Enterprise Plus – The full flagship vSphere edition with all features. Licensed per-CPU socket with no core limits. Enables clustering, live migration, disaster recovery and other advanced capabilities.

Each vSphere ESXi edition is built on the same hypervisor core engine. Higher editions unlock additional enterprise-class capabilities, performance tuning tools and the latest features. Most organizations will run either ESXi Standard or Enterprise Plus editions.

vSphere optional add-on software bundles

In addition to vSphere ESXi hypervisor licenses, VMware offers several performance and availability enhancement bundles:

vSphere with Operations Management – Adds monitoring, alerting and predictive analysis on utilization and performance data for health awareness.

vSphere Distributed Resource Scheduler (DRS) – Allows intelligent load balancing by dynamically moving workloads between hosts using live vMotion migration to reduce bottlenecks and power consumption.

vSphere High Availability (HA) – Provides automated restart of virtual machines on other available ESXi hosts in a cluster during either a hardware failure or host operating system crash. Eliminates downtime from planned/unplanned maintenance.

VMware hypervisor vs virtualization on other platforms

Let’s contrast running the VMware ESXi hypervisor with some alternatives:

Azure and AWS Hypervisors – Public cloud providers use their own proprietary hypervisor technologies not available to customers. You don’t have visibility below the virtualization management layer as the underlying infrastructure is fully managed for you.

Desktop Hypervisors – Platforms like VMware Workstation, VirtualBox and Hyper-V are designed primarily for running VMs on Windows or Linux PCs. They work well enough for development/testing but lack the advanced features, performance, scalability and reliability needed for enterprise production environments.

Kernel-based Virtual Machine (KVM) – The KVM hypervisor is built into the Linux kernel itself as an open-source Type 2 hosted virtualization option. It offers good performance but can’t match proprietary bare metal hypervisors in efficiency, features and centralized management capabilities.

For most robust business-critical virtualization, VMware vSphere ESXi remains an industry leader. The hypervisor’s tiny footprint, extensive ecosystem and unified management via vCenter keep it a top choice for flexible provisioning of virtual workloads.

Key takeaways

  • A hypervisor creates and runs virtual machines, allowing multiple guest operating systems to efficiently share host hardware resources.
  • The VMware ESXi hypervisor installs directly onto physical servers enabling near-native performance and security with a small attack surface.
  • Key components like the VMkernel mediate virtual machine access to actual underlying hardware resources.
  • VMware vSphere enterprise editions unlock advanced virtualization features like live migration, high availability and distributed resource scheduling.


VMware’s vSphere ESXi has proven itself as an extremely reliable, high performance bare metal hypervisor. Its Type 1 architecture efficiently provisions hardware resources to virtual machines while securely isolating workloads.

Rich ecosystem integrations, unified management under vCenter and features like vMotion make vSphere the right choice for business-critical virtual infrastructure initiatives. As more workloads move to the software-defined data center, flexible hypervisor technologies like vSphere ESXi will continue delivering business value reducing costs and improving resiliency.


  1. What’s the difference between a hypervisor and a virtual machine?
    A hypervisor is the software layer that creates and runs virtual machines. A VM is an emulation of a complete computer system that runs its own operating system and applications isolated from other VMs.

  2. Is VMware ESXi free?
    Yes. VMware offers a free edition of ESXi that supports up to 8 physical CPU cores. For full functionality, enterprises usually run the Enterprise Plus edition.

  3. Can you run VMs on bare metal?
    Not efficiently. A hypervisor is required to virtualize hardware, manage resources, isolate VMs and enable advanced capabilities like live migration and high availability clustering.

  4. What OS runs on ESXi?
    As a bare metal Type 1 hypervisor, ESXi runs directly on server hardware without needing its own complete operating system. The tiny VMkernel provides CPU scheduling, memory management and other critical services.

  5. Is VMware ESXi an operating system?
    No. ESXi installs on bare metal without an OS layer. The VMkernel isn’t considered a full-fledged OS but instead a specialized layer that sits between virtual machines and hardware.

  6. Can you convert physical server to VM?
    Yes, through a process called physical to virtual (P2V) conversion. This involves running migration software tools to package up the OS, applications, data and configuration into a set of VM files.

  7. How is bare metal server different than a VM?
    Bare metal indicates a physical server not sharing resources using virtualization. VMs allocate dedicated virtual hardware to emulate full systems. Bare metal servers have no hypervisor layer in between.

  8. Can VMs improve security?
    Yes. By isolating workloads, hypervisors limit potential vulnerabilities and lateral movement between VMs even if one gets compromised. Additional safeguards block unauthorized communication channels.

  9. What’s the difference between shared, dedicated and private hypervisors?
    Shared or multi-tenant hardware pools dynamically allocate hypervisor resources on-demand to VMs. Dedicated hypervisors isolate defined physical hosts to particular groups of VMs. Private cloud can fully reserve infrastructure.

  10. Why are IT organizations adopting hyperconverged infrastructure solutions?
    HCI’s software-defined approach simplifies deployment by tightly integrating compute, storage, networking and virtualization layers into a unified system with centralized management. This increases flexibility while reducing infrastructure costs.

  11. Is network virtualization the same as NFV (Network Functions Virtualization)?
    No. Network virtualization abstracts physical networks from virtual networks. NFV looks to transition networking devices like routers and load balancers that traditionally ran on proprietary hardware into software applications.

  12. What’s the difference between VMware vSphere ESXi and VMware Workstation?
    VMware vSphere ESXi is a bare-metal enterprise-grade hypervisor for running production workloads. VMware Workstation is a Type 2 desktop hypervisor used by admins for application development, testing and training.

  13. Does VMware ESXi include vCenter Server?
    No. vCenter Server provides unified management, orchestration, provisioning, and automation capabilities across multiple ESXi hosts. It is licensed separately while ESXi licenses enable the hypervisor functionality.

  14. Can you manage ESXi without vCenter?
    Yes, ESXi hosts include a direct console and APIs for configuration without vCenter Server. But you lose out on advanced monitoring, automation and orchestration features of the vSphere management layer.

  15. What hardware resources does an ESXi hypervisor require?
    At minimum, 64GB storage, 4GB RAM and 2 CPU cores. Additional resources are allocated to VMs. Enterprise production deployments use multicore processors, 512GB+ storage and at least 128GB memory.

  16. What are the most common use cases for VMware ESXi in the enterprise?
    Server consolidation to reduce hardware costs, improved resiliency via clustering, accelerated deployment of standardized templates, enhanced security isolation for untrusted workloads and supporting business continuity failover scenarios.

  17. What’s the difference between cold, warm and hot migration of VMs?
    Cold migrations require fully powering down the VM during the transfer. Warm migrations keep the VM running but pause it briefly. Hot migration via vMotion eliminates any interruption allowing continuous access.

  18. Can you run Nest virtualization on top of VMware ESXi?
    Yes, hypervisors that meet architectural requirements can run nested, allowing you to build testing/staging environments isolated from production infrastructure. Useful for training, security evaluations, and proofs of concept.

  19. How does VMware Fault Tolerance provide high availability?
    FT provides continuous availability by creating a live shadow instance that automatically keeps pace with the primary VM if running on a separate ESXi host. This shadow VM immediately takes over if the host fails.

  20. What is Distributed Power Management (DPM)?
    An feature that automatically optimizes ESXi host power consumption across a cluster during periods of low resource demand. It consolidates workloads and places unused hosts in standby improving data center energy efficiency.

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