The Cisco 3945E, 3925E, 3945, and 3925 ship with a default memory of 1-GB DRAM and 256-MB Compact Flash. The 1-GB DRAM configuration is derived by the installation of two symmetrical dual in-line memory modules (DIMMs) of 512 MB in each of the memory slots on the SPE of the Cisco 3900 Series platforms. When upgrading memory to higher densities, both memory slots must be populated with DIMMs of symmetrical type and density for high system performance. The Cisco 3900 Series does not support the use of different DRAM densities in the two available DIMM slots or the use of only one slot.