The ES47 consists of one or two drawers, each containing a CPU building block. A building block consists of 2 CPUs and memory. Drawers are joined together using two thick cables, known as the North-South cables. An unusual aspect of the AlphaServer ES47 is its memory subsystem. Not only does it use the uncommon RAMBUS RIMMs, but it also requires memory to be installed in groups of 5 RIMMs. These 5 RIMMs are grouped into a RAID set. In combination with the ECC feature on the RIMMs, this allows for higher fault-tolerance.