It says "Root filesystem" because there can be many other filesystems that are mounted at boot time. Root or /
is like the C-Drive on Windows. A filesystem is mounted, when it is accessible to the higher level system functions via it's mountpoint.
About the process of mounting... I don't know how technical an answer you want so please don't feel offended by this over-simplification. This is how I would explain it to my customers: Plugging in a Flashdrive.
- User connects USB Flashdrive
- OS detects "something" is connected to USB-port X
- OS probes the port and finds out, that there is a flash drive
- OS assigns a device node to the device (let's say
/dev/sdb
)
- OS probes
/dev/sdb
and find a partition table with on primary partition
- OS assigns a device node to the partition (let's say
/dev/sdb1
)
- OS probes
/dev/sdb1
and recognizes a FAT32 file system
- OS mounts the file system at
/dev/sdb1
to a new mountpoint (like /media/pendrive/
)
- The content of the file system is accessible to the system and thus to the user
The content of the device (raw data) is just a bunch of zeros and ones. When mounting a device, the system adds something like a "read/write-filter" on top of those zeros and ones, that translates the zeros and ones to actual files and vice versa.
For example: When you save "Hello World" to text file at /media/pendrive
, then the filter translates this according to the file system's rules and in the end a series of zeros and ones and writes to /dev/sdb1
.