VMware ESX Server and ESXi Server.

1. VMware ESXi Server has no service console.
The traditional (full) ESX Server has a special built-in virtual machine called the “service console”.

2. VMware ESXi Server uses RCLI instead of service console utilities.
As ESXi doesn’t have any CLI with VMware-related or Linux utilities, VMware needed to provide a CLI interface to ESXi. What VMware came up with is the Remote Command line Interface (RCLI).

3. VMware ESXi Server is extremely thin = fast installation + faster boot.
The service console has been removed from ESXi, the footprint in memory has been reduced to just 32MB. You can run a hypervisor, allowing you to run virtual machines on your server, with just 32MB of RAM overhead. In comparison, the full ESX Server on disk footprint is about 2GB.

4. VMware ESXi Server can be purchased as an embedded hypervisor on hardware.
While ESXi is so small that it can be easily installed and can even be booted from a USB Flash disk, what is truly unique about ESXi is that it is being sold by hardware vendors as a built-in hypervisor.

5. VMware ESXi Server has a “yellow firmware console”.
Instead of the full ESX Server “service console” boot (which looks like a Linux server booting), ESXi has a tiny “Direct Console User Interface (DCUI)”.

6. VMware ESXi Server has server health status built in.
With ESXi some hardware monitoring features are built into the hypervisor. With ESX Server, this is not yet built in. Instead, you must install hardware monitoring software in the service console.

7. VMware ESXi Server requires fewer patches and less rebooting.
The full ESX server essentially has a modified Linux system as the service console, there are many patches that have to be deployed to keep it secure. With ESXi, on the contrary, the server has very few patches that need to be applied. Because ESXi has no service console and it is considered more secure and more reliable. Security, Reliability, and Maintainability, are all major factor when considering a hypervisor.