Just as there are two versions of Hyper-V, there are two versions of ESX Server: ESX Server 3.5 and the free ESXi. You can download ESXi from https://www.vmware.com/tryvmware/login.php?eval=esxi&t=1, but ESX Server is available only as part of VMware’s VI3 suite. Both products share the same hypervisor architecture, both offer the same level of performance, and both support exactly the same guest OSs. However, ESXi lacks the Linux-based service console that the full ESX Server product offers. ESXi, therefore, is quite small at 32MB in size. (In fact, at the most recent VMworld conference, VMware distributed copies of ESXi on USB keys.) This small footprint makes ESXi easy to install and deploy, and reduces the host’s attack surface and patching requirements. You use the VI3 client to manage ESXi remotely. A detailed comparison of ESXi and ESX Server is available at http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1006543