This lecture delves into the concept of modularization within the same address space, exploring local procedure calls and program objects. It then transitions into the architectural pattern of client-server systems, focusing on Remote Procedure Calls (RPC) as a means to organize systems into clients and servers. The discussion also touches on Representational State Transfer (REST) as a resource-oriented approach to building client-server systems. The lecture emphasizes the benefits and challenges of RPC and REST, highlighting the trade-offs between the two approaches.