Hierarchical Layout.

Breaking components into encapsulated structural units greatly simplified the design process. Once the alu was designed, the rest of the datapath design needed only to be concerned with providing the correct inputs on the input pins, rather than being concerned with all of the internals of the alu. Also hierarchical design can isolate errors and the changes required to fix them. Otherwise, any change to any part of the design would require the entire project to be recompiled.