It would be 32 GB max, the units have 2 DIMM slots, this means that you can add two 16GB modules to achieve the 32 GBs.
Basically it means that max RAM per DIMM slot would be 16Gb and max total RAM supported by the system would be 32GB.
Depending on how the processor is designed it would support certain amount of RAM, right now Intel® decided that 32GB will allow the unit to work properly and stable.
Chances are that future models could support even more.
Regarding RAM/OS, it would only depend if it is 32-bit or 64-bit based, 64-bit would support more than 4GBs, 32-bit up to 4GBs.
Type of RAM supported: DDR4-1866/2133 1.2V SO-DIMM
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