ProLiant BL685c G6 (DDR2-800MHz) 4GB PC2-6400 DDR2 Memory Compaq ProLiant BL685c G6 (DDR2-800MHz) RAM -4GB 240pin PC2-6400 DDR2-800 800Mhz Registered ECC DIMM. The price is for a single stick all systems require this memory in matching pairs must buy and install 2pcs FOR A KIT BUY Qty 2.