Phase-change RAM (PCM) has the advantages of better scaling and non-volatility compared with the DRAM which is expected to face its scaling limit in the near future. There have been many studies on applying the PCM to main memory in order to complement or replace the DRAM. One common limitation of these studies is that they are based on synthetic PCM models. In our study, we investigate the feasibility and issues of applying a real PCM to main memory. In this paper, we report our case study of characterizing the PCM and evaluating its usefulness in the main memory. Our results show that the PCM/DRAM hybrid main memory with a modest DRAM size can give comparable performance to that of the DRAM only main memory. However, the hybrid memory with small DRAMs or large footprint programs can suffer from performance degradation due to the long latency of both PCM writes and write preemption penalty, which requires architectural innovations for exploiting the full potential of PCM write performance.