What are these?

[PohTayToez]

Ok, this is something that I've wondered for a while:

On many power and data transfer cables (mostly USB), I often see a cylinder around the cable. Upon opening it up, there is always what appears to be two very weak magnets or something that I wrapped around the cable.

That black cylinder on the cable is what I'm talking about... what are they and what do they do?

 

[The_Other_One]

I'm pretty sure it just helps cut down on interference. I've removed them from cables and they still worked perfectly. I think it's just one of those "extra measures" that's basically required...

 

[Laptop]

I think its for the camera or printer. But not sure about removing it

 

[kobaj]

Its a ferrite ring, to remove electrical interference.

LINK