The bus controller acts as a cache controller, bus controller, and as a bus connecting the CPU chip, including its embedded L1 and L2 caches, the L3 cache, the system bus, and other ltanium processors. The bus controller coordinates data movement between the L2 and L3 caches and between the L3 cache and main memory. It also coordinates data movement between the caches, main memory, and peripheral devices via the system bus.