The focus of the Security Architecture and Design domain is system architecture. This domain is of critical importance because in many ways the design of a computer system determines its amount of security. Therefore, security professionals should know and understand the underlying technology of computer systems and the various system security guidelines, certifications, and security and assurance ratings that infosec security professionals use. The following list gives you some key areas to focus on:
Layering, data hiding, and abstraction
Memory: Segmentation/rings, types of memory ...