Pseudo file systems in Linux

A pseudo file system does not exists on the hard disk, it exists only in RAM when the system is running. These are primary pseudo filesystems in Linux:

Contains information about the processes running on the system. Processes are listed by PID in this directory along with some additional hardware information (cpuinfo, meminfo, partitions etc.)

Contains information about hardware and kernel modules

Contains actual handles to all devices that are connected to the system. Any piece of hardware thats get picked by udev, which is actual device manager, gets added to /dev. The udev works in conjunction to D-Bus which is data bus service that passes all information about everything going on within system to other services and devices.