Availability Check vs Available to Promise (ATP)

Hi,

I am confused between Availability check vs ATP. What is the difference between these two? It seems to me both also checks for the availability of materials. Which one is more useful?

From the help file, it says

Availability check= A procedure that ensures that there are enough components available for planned or production orders in production planning and production control.

ATP= Function used to check, together with certain basic methods, if a product can be confirmed.

I can't really make out the difference between the two definitions.

I hope someone out there can help clarify.

Thank you.

Rgds,

Sue