We demonstrate a high performance and cost effective cross point memory (CPM) technology for storage class memory(SCM) which consists of 20nm 1S1M (one selector one memory) unit cell for four-deck 256 Gb density. Novel process integration was developed to make a uniform Vt distribution for a sufficient read window margin (RWM) and a corresponding low raw bit error rate (RBER). However, in spite of the successful integration and excellent performances, it is expected that the scalability of the CPM will face the inevitable drawbacks such as severe thermal disturbance (TDB) and smaller write program margin which is due to the scaling limit of phase change memory component in CPM. Therefore SOM (selector only memory) is suggested as the alternative device for the next generation SCM.