I don't agree with the comment about ESXi not running on server hardware older than 3 years. We are typically refreshing hardware every 3 to 4 years but some of that always trickles down to TEST/DEV and it's all still listed on the HCL and supported. Granted at some point it's going to fall off the HCL for the latest version of the hypervisor but your usually on hardware that is over 5 years old at least by that point.
And to Mrgrouchy, you work for Microsoft I assume right? So much false information spewed in that only ever post from you. Sigh....