VMware ESX

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VMware ESX
Authors VMware, Inc.
Web site www.vmware.com/products/esxi-and-esx

VMware ESX — is an enterprise-class, type-1 hypervisor developed by VMware for deploying and serving virtual computers. As a type-1 hypervisor, ESXi is not a software application that one installs in an operating system; instead, it includes and integrates vital OS components, such as a kernel.

After version 4.1, VMware renamed ESX to ESXi. ESXi replaces Service Console (a rudimentary operating system) with a more closely integrated OS. ESX/ESXi is the primary component in the VMware Infrastructure software suite.

The name ESX is an abbreviation of Elastic Sky X.


ESX runs on bare metal (without running an operating system) unlike other VMware products. It includes its own kernel: A Linux kernel is started first, and is then used to load a variety of specialized virtualization components, including ESX, which is otherwise known as the vmkernel component. The Linux kernel is the primary virtual machine; it is invoked by the service console. At normal run-time, the vmkernel is running on the bare computer, and the Linux-based service console runs as the first virtual machine.

The vmkernel is a microkernel with three interfaces: hardware, guest systems, and the service console (Console OS).

VMware ESX is available in two main types: ESX and ESXi, although since version 5 only ESXi is continued[1].

Pic. 1. Architecture

Version History

Version release history:

  • VMware (7 January 2002)

VMware ESX 1.5

  • VMware ESX Server 1.5 (13 May 2002)

VMware ESX 2.0 (21 July 2003)

  • VMware ESX Server 2.0.1 Build 22983 (13 April 2006)
  • VMware ESX Server 2.0.2 Build 23922 (4 May 2006)

VMware ESX 2.5 (14 December 2004)

  • VMware ESX Server 2.5.0 Build 11343 (29 November 2004)
  • VMware ESX Server 2.5.1 Build 13057 (20 May 2005)
  • VMware ESX Server 2.5.1 Build 14182 (20 June 2005)
  • VMware ESX Server 2.5.2 Build 16390 (15 September 2005)
  • VMware ESX Server 2.5.3 Build 22981 (13 April 2006)
  • VMware ESX Server 2.5.4 Build 32233 (5 October 2006)
  • VMware ESX Server 2.5.5 Build 57619 (8 October 2007)

VMware Infrastructure 3.0 (VI3) (5 June 2006)

  • VMware ESX Server 3.0 Build 27701 (13 June 2006)
  • VMware ESX Server 3.0.1 Build 32039 (25 September 2006)
  • VMware ESX Server 3.0.2 Build 52542 (31 July 2007)
  • VMware ESX Server 3.0.3 Build 104629 (8 August 2008)
  • VMware ESX Server 3.0.3 Update 1 Build 231127 (8 March 2010)
  • VMware ESX Server 3.5 (10 December 2007)
  • VMware ESX Server 3.5 Build 64607 (20 February 2008)
  • VMware ESX Server 3.5 Update 1 Build 82663 (10 April 2008)
  • VMware ESX Server 3.5 Update 2 Build 110268 (13 August 2008)
  • VMware ESX Server 3.5 Update 3 Build 123630 (6 November 2008)
  • VMware ESX Server 3.5 Update 4 Build 153875 (30 March 2009)
  • VMware ESX Server 3.5 Update 5 Build 207095 (20 December 2009) This was the last version to support 32-bit systems

VMware vSphere 4.0 (20 May 2009)

  • VMware ESX 4.0 Build 164009 (21 May 2009)
  • VMware ESX 4.0 Update 1 Build 208167 (19 November 2009)
  • VMware ESX 4.0 Update 2 Build 261974 (10 June 2010)
  • VMware ESX 4.0 Update 3 Build 398348 (5 May 2011)
  • VMware ESX 4.0 Update 4 Build 504850 (17 November 2011)
  • VMware ESX 4.1 Build 260247 (13 July 2010)
  • VMware ESX 4.1 Update 1 Build 348481 (10 February 2011)
  • VMware ESX 4.1 Update 2 Build 502767 (27 October 2011)
  • VMware ESX 4.1 Update 3 Build 800380 (30 August 2012)

ESX and ESXi before version 5.0 do not support Windows 8/Windows 2012[2].

VMware ESXi

The vSphere hypervisor, known in many circles as "ESXi"[3], for the name of the underlying hypervisor architecture, is a bare-metal hypervisor that installs directly on top of your physical server and partitions it into multiple virtual machines. Each virtual machine shares the same physical resources as the other virtual machines and they can all run at the same time. Unlike other hypervisors, all management functionality of vSphere is done through remote management tools. There is no underlying operating system, reducing the install footprint to less than 150 MB.

Features Review

Improved Reliability and Security

The ESXi bare-metal hypervisor’s management functionality is in VMkernel, reducing the footprint to 150 MB. This gives it a very small attack surface for malware and over-the-network threats, improving reliability and security.

Streamlined Deployment and Configuration

With few configuration options and simple deployment and configuration, the ESXi architecture makes it easy to maintain a consistent virtual infrastructure.

Reduced Management Overhead

vSphere ESXi uses an agentless approach to hardware monitoring and system management with an API-based partner integration model. Management tasks are on remote command lines with the vSphere Command Line Interface (vCLI) and Power CLI, which uses Windows PowerShell cmdlets and scripts for automated management. Simplified Hypervisor Patching and Updating

Technical Details

Improved Security

Improved role-based access and control eliminates the dependency on a shared root account. Users and groups can be assigned full administrative privileges. There's no need to share access or a common super user account in order to perform administrative tasks.

Extensive Logging and Auditing

vSphere ESXi logs all user activity from both the Shell and the Direct Console User Interface under the user's account. This logging ensures user accountability and makes it easy to audit user activity.


VMware vSphere live migration allows you to move an entire virtual machine from one physical server to another, without downtime. Customers can migrate live virtual machines across clusters, distributed switches, vCenters and over long distances of up to 100 ms RTT.

Virtual Machine Capabilities

  • Virtual machines running on vSphere ESXi come with support for the following features and capabilities:
  • Virtual machines can support up to 128 virtual CPUs.
  • Virtual machines can support up to 4 TB of RAM.
  • New xHCI controller supports USB 3.0 devices.
  • New Advanced Host Controller Interface (AHCI) supports up to 120 devices per virtual machine.
  • Maximum VMDK size is 62 TB.
  • Guest OS Storage Reclamation returns disk space to the storage pool when it's de-allocated from within the guest OS.
  • Improve CPU virtualization by exposing more information about the host CPU architecture to virtual machines. This improved CPU exposure allows for better debugging, tuning and troubleshooting of operating systems and applications within the virtual machine.
  • Increased CPU efficiency through support of Large Receive Offload (LRO) that aggregates incoming TCP packets into a larger single packet.

Active Directory Integration

You can join vSphere ESXi hosts to your Active Directory domain. Once added, Active Directory handles user authentication and removes the need to create local user accounts on each host. Centralized Management of Host Image and Configuration via Auto Deploy[5] Combining the features of host profiles, Image Builder and PXE, VMware vSphere Auto Deploy simplifies host installation and upgrade. The Auto Deploy library centrally stores all vSphere host images. Administrators can automatically provision new hosts based on user-defined rules and host rebuilds are as simple as a reboot.

Stateless Firewall

vSphere ESXi features a service-oriented and stateless firewall, which you can configure using the vSphere client or at the command line with ESXCLI. The firewall engine allows administrators to define port rules for services. Additionally, you can specify IP ranges or individual IP addresses that can connect to host services.

Known limitations

Known limitations of VMware ESXi, as of April 2015, include the following:

Infrastructure limitations

Some maximums in ESXi Server 6.0 may influence the design of data centers:

  • Guest system maximum RAM: 4 TB
  • Host system maximum RAM: 6 TB (12 TB on certain certified OEM hardware platforms)
  • Number of hosts in a high availability or Distributed Resource Scheduler cluster: 64
  • Maximum number of processors per virtual machine: 128
  • Maximum number of processors per host: 480
  • Maximum number of virtual CPUs per physical CPU core: 32
  • Maximum number of virtual machines per host: 1024
  • Maximum number of virtual CPUs per fault tolerant virtual machine: 4
  • Maximum guest system RAM per fault tolerant virtual machine: 64 GB
  • VMFS5 maximum volume size: 64 TB, but maximum file size is 62 TB

Performance limitations

In terms of performance, virtualization imposes a cost in the additional work the CPU has to perform to virtualize the underlying hardware. Instructions that perform this extra work, and other activities that require virtualization, tend to lie in operating system calls. In an unmodified operating system, OS calls introduce the greatest portion of virtualization "overhead".

Paravirtualization or other virtualization techniques may help with these issues. VMware developed the Virtual Machine Interface for this purpose, and selected operating systems support this. A comparison between full virtualization and paravirtualization for the ESX Server shows that in some cases paravirtualization is much faster.


  1. Training Resources & Documentations
  2. VMware Compatibility Guide
  3. ESXi Developer page
  4. vMotion
  5. Auto Deploy