electromagnetic interference

What is the purpose of the small connector on an HDMI cable?
you've probably noticed it before – a small cylindrical object surrounding the connector of an hdmi cable. most people will ignore it and use the cable for its original purpose, but that little cylinder is actually trying to solve a real technical problem.
What effect does the black bureau on the laptop charger cord have?
near the end of the laptop charging cord there is a black cylinder called a ferrite bead, which is responsible for blocking electromagnetic interference from a device and to a device.