Memory Option # Manufacturing Part # Description Previous Part # SE6X2A11Z 4GB Memory Expansion (2 × 2GB) X-Option, 371-4656 2GB DDR3-1333/PC3-10600 DIMM, n/a SE6X2B11Z 8GB Memory Expansion (2 × 4GB) X-Option, 371-4872 4GB DDR3-1333/PC3-10600 DIMM, n/a SE6X2C11Z 16GB Memory Expansion (2 × 8GB) X-Option, 371-4658 8GB DDR3-1333/PC3-10600 DIMM, n