Root filesystem

§INITRD

RAM at boot. Everything under "/" lives in memory. Limited space

§INITRAMFS

Filesystem lives inside kernel image (image.ub). Fully RAM based. even more single image than INITRD

§UBIFS

Root fileystem stored on raw NAND flash. Persistent storage

§NFS

Root filesystem is on network server. Your board mounts "/" over ethernet on boot

§EXT4

Root filesystem on normal Linux fileystem on disk. stored on SD card partition like /dev/mmcblk0p2. Persistent storage