Motherboards on Desktops have similar form factors,
conversely the motherboards for laptops have different
form factors and are unable to be interchanged.
Components for a motherboard that are made for a laptop
cannot be used with a desktop.
Additionally, the laptops use SODIMMs (Small Outline Dual In-Line
Memory Modules), as opposed to normal RAM cards, to conserve space.
CPUs
Laptop CPUs are designed to produce less heat than desktop
CPUs, as such they require smaller cooling systems to operate
effectively.