Difference between 8GB,4Gx1 + 4G onboard, DDR4, 2666MHz and 8 GB, LPDDR3, 2133 MHz, Integrated?

I have come across two Dell Laptops having the below RAM configuration.

1. 8 GB,4Gx1 + 4G onboard, DDR4, 2666MHz and
2. 8 GB, LPDDR3, 2133 MHz, Integrated

My concern is that 8 GB,4Gx1 + 4G onboard, DDR4, isn't this an 8GB RAM.? or just a 4GB RAM? I read many articles on internet but couldn't understand the difference between these two and which one should be preferred?

Secondly, all the configurations are same in these laptop and only difference is the RAM only. I understand DDR4 is better than LPDDR3?

Laptop 1: New Dell Inspiron 14 5490

Laptop 2: New Dell Inspiron 13 5391

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