What is importance of RAS and CAS in SDRAM?
SDRAM acquires its address command into two address words. This uses a multiplex scheme to save input pins. The initial address word is latched within the DRAM chip along with the row address strobe (RAS).
By follow the RAS command is the column address strobe (CAS) for latching the second address word. In a while after the RAS and CAS strobes, that the stored data is valid for reading.