SpritesMind.Net

Hi I'm new on the genny community.
I would like to know if someone have looked at the bios(tmss?), and tried to replace it ?
I have read on smspower.org that some people made did some hack for the master system, is it possible to do the same in the megadrive ?
In the documents i've found none of them talk about the bios storage ?
Is it stored in a rom ?

The TMSS ROM lives inside a gate array or an ASIC, there are means to bypass it and then add an external chip that does your own thing but it is more trouble than it's worth.

Something like that can be made using the expansion port ? using it as a "hidden" cart port ?