The very first component that you will install in a fully virtualized VMware environment is the ESXi hypervisor. It is a bare-metal installation of VMware's hypervisor on the server hardware.
The installation of ESXi 5.5 is pretty straightforward. It is recommended that you refer to the VMware Compatibility Guide web page to verify whether the server hardware is compatible with ESXi 5.5; this is available at http://www.vmware.com/resources/compatibility/search.php.
For a complete list of hardware requirements, refer to the ESXi Hardware Requirements section on page 13 of the vSphere Installation and Setup guide, available at http://bit.ly/vSphere55_install_guide.
Follow these steps to download the DVD image: