The three Y principles: 'Hierarchy', 'Modularity' and 'Regularity', make computing digestible, accessible, and efficient, in more situations, and for more categories of users.
Systems are divided into modules, which in themselves are again divided into modules, etc., with the final parts being easier to oversee and control.
Modules are aimed at having clearly defined functions, and interfaces that can easily be connected to one another without unpredictable effects.
Modules are made according to uniformity and have to be universally applicable, so that they can be used in many cases, and repeatedly, so that one needs to build fewer modules overall.