What are the three personnel branches in the U.S. Army and how do they relate to each other?

Are you sure that Personnel Command at HQ and the Secretariat not divided into Enlisted Personnel, Officer Corps, and Civilian Work Force? I think what you might have answered is the operational division of units and their personnel at the maneuver level.

PO1 (Join to see) - yes, I'm sure. These three divisions of the branches each have enlisted/NCO and officer management living inside the branch and the branches in that field living together at HRC. The Civilian Workforce management has no touch point with the military personnel management at HRC. We do not have HQ personnel command (PERSCOM), it was replaced by HRC. His question is worded ambiguously and has no other context. So not really sure what he is actually asking.

It was so they could farm finance out to BN S1. IPSA or something like it

This is not new. It has been attempted several times. I am retired army and later held a senior personnel related position as a civilian. Helped block an attempt in the late 90s, early 2000s. The finance community wanted to transfer several tasks to the Army personnel system without giving up positions to support the transfer. This block came back to bite me. The senior staff member leading the charge to transfer the tasks later became my boss. Well needless to say there were some tense moments.

I noticed one of the problems of an integrated system is the programmers did not know the Finance and Personnel business rules.

Enlisted, Warrant and Commission. The civilians are not part of the Army but rather contractors.

SSG Brian G. - Not all civilians are contractors, but I will agree they are not part of the Personnel system per se.