I have a stack of oldish Dell PowerEdge R805 servers that have been running ESX and then ESXi 5.0 on a standard hard drive configuration. Now that they'll not be in production use I was giving them a once over and saw they had an internal 1G SD card that was off in the BIOS.
I decided to turn it on and install ESXi 5.1 on the SD card. I'm pretty sure that the version of ESXi preinstalled was the OEM embedded Dell 3.0 version of ESXi. The 5.1 installer throws quite the fit when doing the check of what's running in the card but it looks like it installs and runs just fine. Mostly python and libparted, see screenshot.
"The selected storage device contains ESX(i). The version could not be determined. Only installation is possible." Fine by me.