The computation speed of computer systems is getting faster and the memory has been enhanced in performance and density through process scaling. However, due to the process scaling, DRAMs are recently suffering from numerous inherent faults. DRAM vendors suggest In-DRAM Error Correcting Code (IECC) to cope with the unreliable operation. However, the conventional IECC schemes have concerns about miscorrection and performance degradation. This paper proposes a pin-aligned In-DRAM ECC architecture using the expandability of a Reed-Solomon code (PAIR), that aligns ECC codewords with DQ pin lines (data passage of DRAM). PAIR is specialized in managing widely distributed inherent faults without the performance degradation, and its correction capability is sufficient to correct burst errors as well. The experimental results analyzed with the latest DRAM model show that the proposed architecture achieves up to 106times higher reliability than XED with 14% performance improvement, and 10 times higher reliability than DUO with a similar performance, on average.