What Is VMware ESXi?
ESXi as a Bare-Metal Hypervisor
VMware ESXi is a bare-metal hypervisor from VMware that is installed directly on server hardware. It runs virtual machines without a general-purpose operating system underneath, which keeps its footprint small and its focus on virtualization.
Because ESXi sits directly on the hardware, it controls CPU, memory, storage and network access itself. That design places it in the type 1 category, and it is one reason ESXi is common in data centers, where a server is expected to run unattended for long periods.
vSphere and vCenter: Managing Many Hosts
ESXi is one part of VMware's vSphere product family. vSphere is the broader suite that includes ESXi along with management and storage features. vCenter Server is the central tool administrators use to manage many ESXi hosts from one place.
Central management unlocks features that are hard to run on single machines. Administrators can group hosts into clusters, share storage between them and move running virtual machines to another host through live migration. These features help when maintenance or hardware failures must not interrupt services.
Where ESXi Fits: Enterprise and Private Hosting
A company that runs its own private cloud is a typical ESXi user. It might operate a cluster of identical servers, each running ESXi, with shared storage and central management. Staff use this environment to run internal applications, databases and development systems, all managed with the same tools.
Hosting providers with large private infrastructure use similar setups. For a comparison with an open source alternative, see KVM vs VMware.
Frequently asked questions
Does ESXi need a separate operating system?
No. ESXi includes its own kernel and management components, so it does not need Windows or Linux beneath it. Administrators usually manage it through vSphere tools or a web interface rather than working inside a general-purpose desktop system.
What is the difference between ESXi and vSphere?
ESXi is the hypervisor installed on each physical host. vSphere is the wider product family that includes ESXi along with vCenter Server and related management tools. A single ESXi host can run on its own, while vSphere is used to run and coordinate many hosts together.