NASM 2.05 based x86 Instruction Reference[ch189]
A.5.167 MOVLPD: Move Low Packed Double-Precision FP MOVLPD xmm,m64 ; 66 OF 12 /r [WILLAMETTE,SSE2] MOVLPD m64,xmm ; 66 OF 13 /r [WILLAMETTE,SSE2] MOVLPD moves a double-precision FP value between the source and destination operands. One of the operands is a 64-bit memory location, the other is the low quadword of an XMM register. The operation of this instruction is: mem(0-63) := xmm(0-63); or xmm(0-63) := mem(0-63); xmm(64-127) remains unchanged.