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What is the thickening closer to one end of the computer cable?

This is a high-pass filter, protection against common mode surges and interference on the cable. Inside this cylinder there are ferrite rings that block the passage of noise, but do not interfere with the signals that are transmitted through this cable to the opposition. Without such a filter on the monitor screen can be ripples and other visual clutter. But if such a cable without protective RF filter intended for another device, there may be failures or even the device will not work due to unavoidable interference.
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