SIS651 is the memory controller.
PC#### memory is backward compatible. Maximum speed is the only significant difference in the specifications. Many manufacturers has stopped making PC2100 memory and will sell you 2700 or better. Again, adding better or higher speed memory does not gain you any additional speed, other than what is gained from the additional memory.
Here is a link to the page in Crusual web site that addresses your computer/motherboard:
Computer memory upgrades for Elite Group (ECS) L4S5MG3 Motherboard from Crucial.com