What is the difference between VMware ESX, ESXi, vSphere and vCenter?

It is quite easy to confuse the VMware products ESX, ESXi, vSphere and vCenter. The purpose of this article is to demistify the whole thing. But first a little background. Virtualization technology allows multiple servers to be installed on the same physical machine. In just the last five years server hardware capability has increased so much that you can virtualize just about any server on the market today. This has enabled organizations to do a lot more with fewer resources.

For those new to VMware a brief explanation of VMware’s core offerings can help to minimize confusion. There are several layers/dimensions: the bare metal server, the hypervisor, the management server and the OS layer. VMware calls the whole thing vSphere but that is a bit confusing.

ESX and ESXi are the hypervisors that most commonly sit right one on bare metal. On “bare metal” means that is the first thing you install on the server before any OS. ESX is used for large scale custom implementations but for most of us ESXi is all you will need because it is easier to configure and more common for typical deployments. In the above picture the bare metal machine is the lowest level indicated by the gray box,  the ESX/ESXi layer is the blue section that says VMware.

ESXi has a tiny footprint when installed and takes up as little as a few hundred MBs on a drive when fully installed. I ran ESXi from a USB stick on a Dell R510 without issue. This is because it is basically just a liaison between the hardware and the OS layers. This is simplifying it for a quick explanation.

ESXi is a fairly uncomplicated to install and configure. Once it is installed and the IP address, subnet, gateway and hostname are configured it is ready to be managed with vSphere Client, the standard VMware management platform.

vSphere is the client application that you use to manage EXSi hosts, VMs and vCenter. It can be installed on any computer including workstations or servers, whether physical or virtual machines. However, if using vSphere to manage ESXi hosts directly without vCenter, you don’t get all the bells and whistles like HA and vMotion.


vCenter Server (installed on Windows) or vCenter Server Appliance (standalone) provide the rich feature set and management components to accomplish much more than the typical hypervisor. There is High Availability and virtualization automation capabilities that make your data center quite resilient.

A newer addition to the ecosystem is the Web Client Plug-in, which supports access to the new features in ESXi and vSphere 5.5 and 6.0. The Web Client is version 5.5 is not as user friendly as the vSphere Client but version 6.0 is big improvement.

If you have not already done so, find an old server, install VMware ESXi and get virtual!