Broadwell-U supports up to 2 channels with an 8GB DIMM per channel.[1] For configurations up to 8GB, you only need to run traces for one channel. Supporting 16G

Broadwell-U supports up to 2 channels with an 8GB DIMM per channel.[1] For configurations up to 8GB, you only need to run traces for one channel. Supporting 16GB requires more design work (need to run twice as many traces) and wastes logic board space on lower-RAM configs. Apparently, Lenovo decided the trade-off wasn't worth it. 1. http://ark.intel.com/products/85212 http://ark.intel.com/products/85212 Edit: If the 2015 X1 Carbon is dual-channel, I'm not sure why Lenovo would lack a 16GB option. I guess mounting twice as many RAM chips could hit space constraints.