Product architecture and architectural capabilities are key components of dynamic capabilities. However, their precise roles in shaping competitive advantage remain unclear. This chapter examines the evolution of product architecture in the US personal computer industry through a comparative analysis of Intel-line PCs and Apple-line PCs. By tracing software, firmware, and hardware developments from the 1970s to 1990s, this study reveals how firms leveraged distinct architectural capabilities to adapt to technological shifts and market demands. Microsoft drove open modularization by strengthening software standardization through combinative capabilities. Conversely, Apple employed integrative capabilities to construct closed modular systems with distinctive interfaces. A key finding is the critical role of firmware in bridging hardware and software, influencing architectural direction. Additionally, this analysis also highlights how cospecialization functioned as a competitive advantage. As modularization enabled low-cost industry assets, companies like Apple and Microsoft adapted these assets differently, fostering architectural diversity. This interfirm competition generated a nexus of dynamic capabilities at the ecosystem level, suggesting that industry leadership emerged not from a single firm, but through the collective interplay of diverse architectural strengths. These findings provide valuable insights into the foundations of innovation and competitiveness in digital product industries.