Herms - rims

I have been doing some searching to research HERMS and RIMS but cannot figure out the difference between a HERMS and a RIMS system and how they work.

I know that wort is circulated during the mash but cannot figure out if it disturbs the grain bed and it doesn't matter or if it is gently returned much like a sparge?

Thanks!

In general:

HERMS - uses a heat exchanger (usually residing in the HLT), mash is circulated through this heat exchanger and deposited back into the MLT. In my case, it's gently returned on the top of the grain bed, doesn't really disturb it much.

RIMS - the wort is circulated to another vessel or RIMS tube and heated while in that vessel. It then returns back to the MLT.

The main difference is one uses a heat exchanger to change the temp of the recirculating wort while the other is heated without a heat exchanger. A RIMS is usually able to perform much quicker steps at slightly higher risk of scorching and the need for another vessel.

Aaahhhhh. Much clearer, thank you.