VMware vSphere and ESX/ESXi often are used interchangeably to describe the bare-metal VMware hypervisor for virtualization.
What's the difference in vSphere vs. ESXi?
VMware calls its hypervisor architecture ESXi or ESX, depending on the version. The hypervisor platform, through which admins manage the ESXi hypervisor, troubleshoot problems, make changes and do other tasks, is the VMware vSphere software suite.
The bare-metal ESXi hypervisor is an operating system-independent way to virtualize physical data center resources into pools hosting multiple virtual machines (VMs). To be clear, when you're comparing ESXi vs. vSphere, vSphere is the software platform that runs atop an ESXi architecture and is available in various editions. This is analogous to architectural specifications and the buildings created on those plans. With vSphere, ESXi-operated hosts interact with storage and network resources, backup tools and monitoring and management software, among other IT resources.
VMware's vSphere virtualization platform undergoes periodic revisions and updates, with added application programming interfaces and features as well as changes to the ESXi shell. VMware vSphere is also a necessary component for the vCloud Suite for cloud computing.
VMware offers vSphere in several editions -- Standard, Enterprise and Enterprise Plus -- with more features in the higher-level editions. All of the vSphere editions operate on ESXi hosts.
The ESXi hypervisor architecture does not come in Standard, Enterprise or Enterprise Plus editions. However, there are two architecture formats, both offering bare-metal virtualization: the older ESX and the current ESXi. The main difference in ESX vs. ESXi is that ESX uses a console operating system for management functions and ESXi does not.
To make matters more complicated, VMware offers a free hypervisor for newcomers to virtualization, named the vSphere ESXi hypervisor, or vSphere Hypervisor. While it lacks features of the paid editions of vSphere, this hypervisor set-up offers virtualization with minimal requirements and expenditures.
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