For almost 30 years, computer memory systems have been essentially the same: volatile, high speed memory technologies like SRAM and DRAM used for cache and main memory; magnetic disks for high-end data storage; and persistent, low speed flash memory for storage with low capacity/low energy consumption requirements such as embedded/mobile devices. Today we watch the emergence of new non-volatile memory (NVM) technologies that promise to radically change the landscape of memory systems. In this work we assess system-level latency and energy impacts of a computer architecture with persistent main memory using PCRAM and Memristor. Our experimental results support the feasibility of employing emerging non-volatile memory technologies as persistent main memory, indicating that performance penalties should be mild, and energy improvements should be significant, up to 45.5% less when using PCRAM and 72.4% less when using Memristor.