VMware ESXi (formerly 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.[2]

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.[3]

The name ESX is an abbreviation of Elastic Sky X.[4][5]


ESX runs on bare metal, without running an operating system,[6] unlike other VMware products.[7] It includes its own kernel: A Linux kernel is started first,[8] and is then used to load a variety of specialized virtualization components, including ESX, which is otherwise known as the vmkernel component.[citation
] 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. VMWare dropped development of ESX at version 4.1, and now uses ESXi, which does not include a Linux kernel.[citation

The vmkernel is a microkernel[9] with three interfaces: hardware, guest systems, and the service console (Console OS).

vMotion: live migration

Live migration (vMotion) in ESX allows a virtual machine to move between two different hosts. Live storage migration (Storage vMotion) enables live migration of virtual disks on the fly.[19] During vMotion Live Migration (vLM) of a running virtual machine (VM) the content of the (RAM) memory of the VM is sent from the running VM to the new VM (the instance on another host that will become the running VM after the vLM). The content of memory is by its nature changing all the time. ESX uses a system where the content is sent to the other VM and then it will check what data is changed and send that, each time smaller blocks. At the last moment it will very briefly ‘freeze’ the existing VM, transfer the last changes in the RAM content and then start the new VM. The intended effect of this process is to minimize the time during which the VM is suspended; in a best case this will be the time of the final transfer plus the time required to start the new VM.[20][21]

VMware ESXi

VMware ESXi is a smaller footprint version of ESX that does not include the ESX Service Console. It is available without the need to purchase a vCenter license as a free download from VMware with some features disabled.[25][26][27]

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. The same installation media will install to either one or the other of these installation modes depending on the size of the target media.[28] It has the ability to upgrade to VMware Infrastructure 3[29] or VMware vSphere 4.0 ESXi.

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

To virtualize Windows 8 or Windows Server 2012 as guest operating systems, the ESXi version must be 5.0 update 1 or later.