[CentOS] Does devtmps and tmpfs use underlying hard disk storage or Physical Memory (RAM)

Hi,

I am running the below command on CentOS Linux release 7.6.1810 (Core)

# df -hT --total Filesystem Type Size Used Avail Use% Mounted on /dev/xvda1 xfs 150G 8.0G 143G 6% / devtmpfs devtmpfs 7.8G 0 7.8G 0% /dev tmpfs tmpfs 7.8G 0 7.8G 0% /dev/shm tmpfs tmpfs 7.8G 817M 7.0G 11% /run tmpfs tmpfs 7.8G 0 7.8G 0% /sys/fs/cgroup tmpfs tmpfs 1.6G 0 1.6G 0% /run/user/995 tmpfs tmpfs 1.6G 0 1.6G 0% /run/user/1000 total - 185G 8.8G 176G 5% - #

Does devtmpfs and tmpfs use underlying hard disk storage or does it uses Physical Memory (RAM). What is the purpose of devtmpfs which is mounted on /dev, tmpfs mounted on /dev/shm and so on and so forth. What is the difference between devtmpfs and tmpfs?

I will appreciate if anyone can help me understand the above output.

Thanks in Advance and i look forward to hearing from you.

Best Regards,

Kaushal