This afternoon I attended a talk at MPI of Yurii Aulchenko about his R package genABEL. He uses a nice trick to convert genotypes into 8 bit (as there are is no 2 bit format 00,01,10,11) which saves quite a lot of memory.
And here is the E type that I have seen a couple of months ago:
CC-BY-NC Science Surf , accessed 01.04.2026, click to save as PDF