Owner's Manual (PDF)
Page 28
... connectors 3 and 4. Otherwise, your computer during a memory upgrade, keep them separate from any new module(s) that you may have, even if you purchased the new module(s) from Dell. Recommended memory configuration: Type Slots 1600 MHz DDR3 Slots 1 and 2 or slots 1 through 4 28 Memory Module(s) CAUTION: If you remove the original memory module(s) from your computer may not boot.
... connectors 3 and 4. Otherwise, your computer during a memory upgrade, keep them separate from any new module(s) that you may have, even if you purchased the new module(s) from Dell. Recommended memory configuration: Type Slots 1600 MHz DDR3 Slots 1 and 2 or slots 1 through 4 28 Memory Module(s) CAUTION: If you remove the original memory module(s) from your computer may not boot.