Personnel in general refers to a body of persons employed in an organization or place of work. It includes every one starting from the top man (chief executive) to the lowest paid employee, as can be understood from the following sentences.
The company has provided all personnel with proper identity card.
Everyone from airport personnel to travelers will be alert for suspicious signs.
This is a notice to all Personnel.
Staff refers to persons who are in positions to discharge supporting function, such as a group of assistants to a manager, executive, or other person in authority, as;
The Chairman has his personal staff comprising of a Staff officer, Protocol Officer, Private Secretary, Personal Assistant, who are responsible to assist the Chairman in all the matters.
A group of military officers assigned to assist a commanding officer in an executive or advisory capacity are also called staff.
In an organization (large company), there are Line as well as staff positions. A line position is one in which the individuals responsibilities include those that are directly involved with the purpose of the organization. This does include management. Staff positions on the other hand is simply a position that supports the line position.