can use ddr3 in ddr4 slot
Key difference between DDR4 and DDR3 RAM
Physically, a DDR4 module, looks very similar to a DDR3. However, DDR4 has 288 pins compared with DDR3’s 240 pins; DDR4 SO-DIMMS have 260 pins instead of 204 in DDR3
PC Desktop DDR 2/DDR 3 RAM Memory Slot tester
This difference in notch position is also why you can't use DDR3 RAM in a DDR2 system or install DDR2 RAM into a DDR3 slot (even though they have the same number of pins).
Những lưu ý khi thay thế, nâng cấp RAM laptop. Máy tính DND
System Memory 2GB DDR3 (1 x 2GB) Maximum Memory 16GB Memory Slots 2 x SODIMM DDR3 (Note: For dual-DIMM configurations, you must use a pair of identical DDR3 ...