In the Marines the enlisted rank splits, could someone explain this?

Whats the difference between a Gunnery sergeant and a sergeant Major?In the Marines the enlisted rank splits, could someone explain this?
Up to Gunnery Sergeant (E-7) there is one path.





After that, you make a decision whether to stay in your MOS (your job/specialty) or switch to the administrative side of things.





When getting promoted to E-8 you either become a Master Sergeant (stay in your MOS) or switch to admin and become a First Sergeant (also E-8).





First Sergeants then get promoted to Sergeant Major (E-9) and Master Sergeants get promoted to Master Gunnery Sergeant (E-9). You can even have more than one, although generally one will be in charge.





There is only one First Sergeant and one Sergeant Major for each unit, so there are significantly fewer slots to fill on the admin side; whereas each specialty can have its own Master Sergeant and Master Gunnery Sergeant.





When you need to know when the next formation is, ask the First Sergeant. When its time to get yelled at because you did not wear something right, see the SgtMaj.





When you want to know the best way to do your job, ask the Master Sergeant or Master Gunnery Sergeant.





(I exagerate slightly here to illustrate. Don;t worry, your Sgt will tell you all you need to know - whether you want him to or not.)In the Marines the enlisted rank splits, could someone explain this?
2 paygrades and ranks.





A Gunnery Sergeant is an E-7





A Sergeant Major is an E-9





In the middle of those is Master Sergeant/First Sergeant which is an E-8
Splits?


A Gunny is an E-7. A Sergeant Major is an E-9.