Описывается процесс загрузки ядра
The Linux kernel must mount the root filesystem in order to get to the next step and to make the system useful. However, it is possible that the root filesystem exists on a device that the kernel does not know how to support. The solution to this is the initial RAM disk initrd. The kernel drivers necessary to continue the boot are bundled into the filesystem that is stored beside the kernel itself in /boot. The kernel boots, mounts the initrd, loads the drivers inside, and then remounts the real root filesystem using the new drivers. This allows drivers to be added to the kernel easily and for the kernel to mount the root filesystem over almost any storage hardware—even if it’s via a network.
Вопрос вот в чем: зачем монтировать раздел, добавлять в него драйверы для перемонтирования корневого раздела? Разве все драйвера уже не находятся в ядре?