The core-engine of YaST consists of some binary components (modules) that are interconnected via YaST-specific protocols. There are clients as well as servers that are responsible for specific tasks that may have to be accomplished during a YaST-session. According to the well-known client-server-paradigm often used in software technology, YaST-servers are program modules that passively await connections from certain clients to process their requests. Clients on the other hand are active components that send requests to the servers thereby initiating certain actions.

For example the SCR and the UI act as server components that process client-requests on demand. An example for a client module is the stdio-component that can be used to connect the YaST-internal communication with a terminal.

Because this architectural specialty is meant to be used only by the YaST core developers to establish and maintain the low-level machinery we will not go into more detail here. Instead we will focus on the advocated method of extending YaST at the “open end” by creating YCP-modules.