[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