y'all remember that period of time where ESXi was the be-all end-all of virtualization? so much so that several big computer hardware companies put SD card slots onto the server motherboard directly.
and not just ONE, but multiple, in a RAID mirror configuration, in case one of the SD cards, as they were kinda likely to do in that era, would just shit the bed, you wouldn't have an unbootable ESXi server.
We lived in wild times.