If you are looking for information on "emummc" (specifically for portable gaming handhelds like the Nintendo Switch), this refers to a that allows you to run an entire operating system (MMC) from an SD card rather than the console's internal memory.
Are you looking to an existing emuMMC to a new SD card, or are you starting a fresh installation ? Homebrew Switch EmuNand Setup Guide emummcini portable
To keep your emuMMC "clean," ensure you have a emummc.txt file in sdmc:/atmosphere/hosts/ to block Nintendo's servers. If you are looking for information on "emummc"
to tell the system to use the emuMMC instead of the internal storage. Points to the folder containing your emuMMC files (e.g., emummc/SD00/eMMC nintendo_path: emummcini portable
+230 ms boot time due to partition scan (negligible).