User Manual
Page 26
... Channel Channel A Channel B Sockets DIMM_A1 DIMM_B1 Install a memory module in DIMM_A1 slot to prevent installation on a DDR DIMM socket. A DDR2 module has the same physical dimensions as a DDR DIMM but has a 240-pin footprint compared to the 184-pin DDR DIMM.
... Channel Channel A Channel B Sockets DIMM_A1 DIMM_B1 Install a memory module in DIMM_A1 slot to prevent installation on a DDR DIMM socket. A DDR2 module has the same physical dimensions as a DDR DIMM but has a 240-pin footprint compared to the 184-pin DDR DIMM.