what do these do on usb cables and others

[jaystarter]

Is there a reason why on some monitor cables and usb cables there are these "lumps" (see pic) while others are plain. I have used both to connect the same peripherals and there doesn't appear to make any difference to the the workings. I would be interested to know just what they do.

[jonwallace]

They are ferrite beads to suppress interference. Look here.

Interestingly, the very short cable for my sansa clip+ MP3 player has a bead, but even a longer cable that's beadless transfers music quite nicely.

[Leif]

...and there doesn't appear to make any difference to the the workings. I would be interested to know just what they do.

John's link explains why they are there and as it explains, what is not often appreciated is what they can do with respect to third party electronics. They may not have an effect on the transfer of your data, but they could well make a difference to the integrity of your mobile 'phone reception, an adjacent wireless network, your pacemaker....
Suppression is not just about limiting interference coming in, but on what goes out. Antennae transmit as well as receive, and my understanding of why they are they is to prevent interference going out as opposed to protect against it coming in.

[StuartR]

I used to have a problem that when I plugged my mobile phone charger into a socket in my car it caused very annoying interference on the radio. I removed one of these ferrite beads from an old power supply that was not in use and attached it to the mobile phone charging lead - this resulted in a major improvement to the car radio reception.

[jonwallace]

Suppression is not just about limiting interference coming in, but on what goes out. Antennae transmit as well as receive, and my understanding of why they are they is to prevent interference going out as opposed to protect against it coming in.

Oh, so they're there to protect everyone from my Shane Macgowan tracks... (in-joke to partly explain why my link up there was possibly offensive - if you know about Shane, you'll understand...)

[jaystarter]

Suppression is not just about limiting interference coming in, but on what goes out. Antennae transmit as well as receive, and my understanding of why they are they is to prevent interference going out as opposed to protect against it coming in.

Oh, so they're there to protect everyone from my Shane Macgowan tracks... (in-joke to partly explain why my link up there was possibly offensive - if you know about Shane, you'll understand...)

Ha! As I need subtitles to watch (and laugh at) Rab Nesbit there's not much chance of understanding Shane!