One is retail and one is OEM (System Builder), both OS's are exactly the same but the main differances are that the System Builder licence is attached to the motherboard of the system, so if you ever upgrade the board to a different chipset/model you'll need a new licence as well. You also don't get Micosoft tech support with the system builders version.
By locks to the motherboard mean that it can only be used 1 time? What if I switched PC's would I just Copy the OS onto a SSD?
An OEM license is locked to the first motherboard it is installed on and may not be transferred to another, except in the case of a motherboard failure where the replacement is an exact replacement (make, model).
Any other use of the key is a violation of the license.