^^^
It's definitely 8GB:
4 x DIMM, Max. 8 GB, DDR3 1800(O.C.)/1600(O.C.)/1333/1066/800 ECC,Non-ECC,Un-buffered Memory
Dual Channel memory architecture
*When installing total memory of 4GB capacity or more, Windows® 32-bit operation system may only recognize less than 3GB. Hence, a total installed memory of less than 3GB is recommended.