The window hierarchy cache keeps information on the current window hierarchy in the primary memory. Windows are stored in an ordered tree structure and window operations are performed on this structure. Window operations typically result in changes to the fields of the nodes in this structure or result in insertions and deletions of nodes. Upon completion of window operations the desktop component is signaled for a screen update. Details on the data structure of the window hierarchy cache is discussed later in this chapter in Section 5.2.1.