Maximized dual-channel performance requires SODIMMs of the same size and speed in both memory slots.
So there are two slots. You have a single 4 gb. It seems odd, but your laptop may actually perform better with 2 x 4 = 8 instead of 4 + 8 = 12. The memory used is DDR4-2400 SO-DIMM. Max memory would be 2 x 16 = 32 gigs.
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