The terminology is confusing and the article isn't doing a good job of explaining it. "Rootfs" is an im-memory virtual filesystem used to hold the root. The bo

The terminology is confusing and the article isn't doing a good job of explaining it. "Rootfs" is an im-memory virtual filesystem used to hold the root. The bootloader will read the initramfs into ram before executing the kernel, then the kernel will use that in memory data to construct the rootfs filesystem. For non root partitions you would use a loopback device or tmpfs. Since system is a normal partition, the kernel can use the normal disk/filesystem drivers as a root device.