What are the things near the end of cables... They are bulbous and an inch or two from the end?

Question

I have them on my laptop power cord, as well as on hdmi cables to the dvd player... they are ubiquitous but I don't know what they do or what they are. You kinow what I'm talking about?

Answer 1

They are called Ferrite beads and are used to reduce high-frequency interference.

Here is agood link
http://en.wikipedia.org/wiki/Ferrite_bead

Answer 2

Usually, they're just magnets encased in plastic. They're on there to prevent interference.