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VMware ESX

VMware ESX is an enterprise-level computer virtualization product offered by VMware, Inc. ESX is a component of VMware's larger offering, VMware Infrastructure, and adds management and reliability services to the core server product. The original ESX is being replaced by ESXi. ESX allegedly stands for "Elastic Sky X".

VMware ESX and VMware ESXi are bare-metal embedded hypervisors that are VMware's enterprise software hypervisors for servers that run directly on server hardware without requiring an additional underlying operating system.

Technical description

VMware, Inc. refers to the hypervisor used by VMware ESX as "vmkernel".


VMware states that the ESX product runs on "bare metal". In contrast to other VMware products, it does not run atop a third-party operating system, but instead includes its own kernel. Up through the current ESX version 4.1, a Linux kernel is started first, and is used to load a variety of specialized virtualization components, including VMware's vmkernel component. This previously-booted Linux kernel then becomes the first running virtual machine and is called the service console. Thus, 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 itself, which VMware says is a microkernel, has three interfaces to the outside world:

  • hardware
  • guest systems
  • service console (Console OS)
Interface to hardware

The vmkernel handles CPU and memory directly, using scan-before-execution (SBE) to handle special or privileged CPU instructions and the SRAT (system resource allocation table) to track allocated memory.

Access to other hardware (such as network or storage devices) takes place using modules. At least some of the modules derive from modules used in the Linux kernel. To access these modules, an additional module called vmklinux implements the Linux module interface. According to the README file, "This module contains the Linux emulation layer used by the vmkernel."

The vmkernel uses the device drivers:

  1. net/e100
  2. net/e1000
  3. net/e1000e
  4. net/bnx2
  5. net/tg3
  6. net/forcedeth
  7. net/pcnet32
  8. block/cciss
  9. scsi/adp94xx
  10. scsi/aic7xxx
  11. scsi/aic79xx
  12. scsi/ips
  13. scsi/lpfcdd-v732
  14. scsi/megaraid2
  15. scsi/mptscsi_2xx
  16. scsi/qla2200-v7.07
  17. scsi/megaraid_sas
  18. scsi/qla4010
  19. scsi/qla4022
  20. scsi/vmkiscsi
  21. scsi/aacraid_esx30
  22. scsi/lpfcdd-v7xx
  23. scsi/qla2200-v7xx

These drivers mostly equate to those described in VMware's hardware compatibility list. All these modules fall under the GPL. Programmers have adapted them to run with the vmkernel: VMware Inc has changed the module-loading and some other minor things.


Large companies might use datacenter for hosts and virtual machines as a primary container. Multiple datacenters can be used to represent organizational/business units......

Service console

The Service Console is a vestigial general purpose operating system most significantly used as bootstrap for the VMware kernel, vmkernel, and secondarily used as a management interface. Both of these Console Operating System functions are being deprecated as VMware migrates to exclusively the 'embedded' ESX model, current version being ESXi. The Service Console, for all intents and purposes, is the operating system used to interact with VMware ESX and the virtual machines that run on the server.

Linux dependencies

ESX uses a Linux kernel to load additional code: often referred to by VMware, Inc. as the "vmkernel". The dependencies between the "vmkernel" and the Linux part of the ESX server have changed drastically over different major versions of the software. The VMware FAQ states: "ESX Server also incorporates a service console based on a Linux 2.4 kernel that is used to boot the ESX Server virtualization layer". The Linux kernel runs before any other software on an ESX host. On ESX versions 1 and 2, no VMkernel processes run on the system during the boot process. After the Linux kernel has loaded, the S90vmware script loads the vmkernel. VMware Inc states that vmkernel does not derive from Linux, but acknowledges that it has adapted certain device-drivers from Linux device drivers. The Linux kernel continues running, under the control of the vmkernel, providing functions including the proc file system used by the ESX and an environment to run support applications. ESX version 3 loads the VMkernel from the Linux initrd, thus much earlier in the boot-sequence than in previous ESX versions.

In traditional systems, a given operating system runs a single kernel. The VMware FAQ mentions that ESX has both a Linux 2.4 kernel and vmkernel — hence confusion over whether ESX has a Linux base. An ESX system starts a Linux kernel first, but it loads vmkernel (also described by VMware as a kernel), which according to VMware 'wraps around' the linux kernel, and which (according to VMware Inc) does not derive from Linux.

The ESX userspace environment, known as the "Service Console" (or as "COS" or as "vmnix"), derives from a modified version of Red Hat Linux, (Red Hat 7.2 for ESX 2.x and Red Hat Enterprise Linux 3 for ESX 3.x). In general, this Service Console provides management interfaces (CLI, webpage MUI, Remote Console). This VMware ESX hypervisor virtualization approach provides lower overhead and better control and granularity for allocating resources[citation needed] (CPU-time, disk-bandwidth, network-bandwidth, memory-utilization) to virtual machines, compared to so-called "hosted" virtualization, where a base OS handles the physical resources. It also increases security.

As a further detail which differentiates the ESX from other VMware virtualization products: ESX supports the VMware proprietary cluster file system VMFS. VMFS enables multiple hosts to access the same SAN LUNs simultaneously, while file-level locking provides simple protection to file-system integrity.

VMware ESXi

VMware ESXi is a smaller footprint version of ESX that does not include ESX's Service Console. It is available as a free download from VMware though certain features are disabled without the purchase of a vCenter license.

VMware ESXi was originally a compact version of VMware ESX that allowed for a smaller 32 MB disk footprint on the Host. With a simple configuration console for mostly network configuration and remote based VMware Infrastructure Client Interface, this allows for more resources to be dedicated to the Guest environments.

There are two variations of ESXi, VMware ESXi Installable and VMware ESXi Embedded Edition. It has the ability to upgrade to VMware Infrastructure 3 or VMware vSphere 4.0 ESXi.

Originally named VMware ESX Server ESXi edition, through several revisions, finally becoming VMware ESXi 3. New editions then followed ESXi 3.5, ESXi 4 and now ESXi 5.

VMware vSphere

VMware vSphere (formerly VMware Infrastructure 4) is VMware's cloud computing virtualization operating system.VSphere Enterprise

While VMware Infrastructure 3.5 was in development, vSphere was conceived as an enhanced suite of tools with cloud computing utilizing VMware ESX/ESXi 4.

The cloud computing-enabled tool suite was spun off as VMware Infrastructure 4 (for short, VI 4) parallel to but distinct from VMware Infrastructure 3.5 (VI 3.5) that was then ready.

VMware eventually announced vSphere 4 instead of VI 4 on April 21, 2009 and released it on May 21, 2009.

VMware released Update 1 for vSphere 4 on November 19, 2009 to add support for Windows 7 and Windows Server 2008 R2.

VMware's vSphere 4.1 began shipping in August 2010. This update included an updated vCenter Configuration Manager as well as vCenter Application Discovery Manager, and the ability of vMotion to move more than one virtual machine at a time from one server host to another.

VMware released Update 1 for vSphere 4.1 on 10 February, 2011 to add support for RHEL 6, RHEL 5.6, SLES 11 SP1 for VMware, Ubuntu 10.10, and Solaris 10 Update 9.

A secret installation of vSphere was used by a disgruntled former employee to wipe out a New Jersey based pharmaceutical company's VMware installation in February of 2011, costing a reported $800,000 loss.

On 12 July 2011, VMware released its latest version of the suite: VMware vSphere 5.

Related products

The following products operate in conjunction with ESX:

  • vCenter Server, enables monitoring and management of multiple ESX, ESXi and GSX servers. In addition, users must install it to run infrastructure services such as:
    • VMotion (transferring virtual machines between servers on the fly, with zero downtime)
    • SVMotion (transferring virtual machines between Shared Storage LUNs on the fly, with zero downtime)
    • DRS (automated VMotion based on host/VM load requirements/demands)
    • HA (restarting of Virtual Machine Guests in the event of a physical ESX Host failure)
  • Converter, enables users to create VMware ESX Server- or Workstation-compatible virtual machines from either physical machines or from virtual machines made by other virtualization products. Converter replaces the VMware "P2V Assistant" and "Importer" products — P2V Assistant allowed users to convert physical machines into virtual machines; and Importer allowed the import of virtual machines from other products into VMware Workstation.
  • vSphere Client (formerly VMware Infrastructure Client), enables monitoring and management of a single instance of ESX or ESXi server. After ESX 4.1, vSphere Client was no longer available from the ESX/ESXi server, but must be downloaded from the VMware web site.


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