On the DSTwo firmware is just a small program that initializes the SD/SDHC card and loads the EOS. Some other cards like the CycloDS include the OS in the firmware while others like the old R4 do not have an updatable firmware at all. I like the DSTwo's method better as there is no risk of bricking due to an OS update (yes, the CycloDS havs a recovery mode but it doesn't always work).