What is 1 x 2 x DIMM Dual Channel DDR3 and socket for expansion

[krystler07]

I have a Laptop model of asus X555UB series and I want to upgrade the RAM. I want my laptop to install its maximum supported ram. My laptop has 4GB of RAM as-is when I bought it.

Here the Manufacturer's specification.
DDR3L 1600 MHz SDRAM, 1 x 2 x DIMM Dual Channel DDR3 1333/1066/800 MHz.
Support MAX 8GB. socket for expansion up to 12 GB SDRAM
-https://www.asus.com/ph/Laptops/X555UB/specifications/

My Laptop Specs:
Intel® Core™ i5 6200U Processor 2.3 GHz up to 2.8GHz
Windows 10 Home
4GB of RAM
NVIDIA® GeForce® 940M with 2GB DDR3 VRAM
1TB HDD - 5400 RPM

I really don't know what does it mean when they say 1 x 2 x DIMM Dual Channel DDR3.
So does my laptop has 2 slots? and only 8GB of RAM stick is the only think that I can install to be 4gb + 8gb= 12gb?

 

[Lutfij]

The laptop/notebook has one onboard/soldered on 4GB of ram. There should be a single available slot for you to expand the ram to 12GB. Mind you you should be looking at a single 8GB DDR3L 1600MHz stick of ram rated to run at 1.35v.

The slot I'm talking about is that seen in this Ebay listing. First image, next to the masked area.

 

[krystler07]

SDRAM?
What if the RAM I bought is tested at 1.5 voltage? Will it still work?