I know that you can't expand your ram because it is intern. But I want a extern memory chip (512mb1024KBytes) that is very fast. I know that I need a library to access information on this chip. And functions to read and write data. A shield or breakout board it doesn't matter, and I want that it is compatible with Arduino mega. If the arduino lost power it doesn't matter if I lost the data. It must hold the data when the arduino is powerd.