Diff Pump? Diff preload?

Hey guys, just a quick one. What do the Diff Pump and Diff preload do in setup options? I had a look around the web and can't really find anything useful. I understand the power and coast settings, but not these two.

Thanks!

 

Check this out mate:

 

edited OP. I meant pump. typo, sorry. Thanks for the preload info!

 

I re-edited my post

 

Thanks a lot mate.