I've been working in computer retail bushiness (as a promoter) and i've been told that Dell started manufacturing it's own unique motherboards and memory ( Ram, HDD..etc). is that correct? I really need answers because the customer deserves to have accurate information about the device he's buying (misleading information) and I also do not want to compromise my credibility.
Dell does not manufacture either system boards or memory. They do what everyone else does - contract the manufacture to the big ODMs (in notebooks, those are Quanta, Compal, Wistron, Pegatron and a couple of others).
Notebook boards are proprietary to the system -- and it's becoming increasingly common for memory to be soldered onto the mainboard rather than installed as a replaceable module. That's true not only for Dell, but for all notebook systems.
ejn63 is correct (as usual!).
We do not manufacture the hardware. Dell uses OEM (original equipment manufacturer) customized hardware purchased from the manufacturer.
For example, concerning Desktop computer video cards, the EVGA GeForce GTX 1080 could be different than the MSI GeForce GTX 1080 or the ASUS GeForce GTX 1080. Nvidia has a base design for the GeForce GTX 1080 that is then changed per the buyers (Dell, EVGA, MSI, ASUS) instructions. Although the labeling, shroud, clock speeds, fan configuration, could be different, it is still a Nvidia GeForce GTX 1080.