System architecture and design

If requirements analysis and definition are about what a system provides, system architecture and design are primarily about how those capabilities work. The differences in how various development methodologies deal with architecture and design is less about that how and more about when they are defined. Essentially, given a set of requirements (the intentions behind the system, or the why), the implementation details (the how) will almost certainly be determined more by those requirements and the specifics of how best to implement them in the programming language than by when they are identified, consolidated, or formalized.