Why we use cross cable between Computer and Router?

both router and Computer NIC card are the same pin arrangment which means both send with pin1 and pin2 and recive on pin3 and pin6 so by using cross over cable we can manage to connect sending pin to Reciving pin in both end but if we use stright through cable we connect sending pin to sending pin/ reciving pin to reciving pin

because they have the MAC address we connect two same devices by cross cable plus that the pc and the router

crossover allows you to be able to transfer data without a router or hub

Between same devices we tend to use cross cable (such as Hub to Hub or Switch to Switch) and for different devices like communication btw computer and switch we use straight cable.

the concept behind the cross or straight reside on TX and RX for both of them they polarize by -/+ so we have -Tx / +Tx as well -Rx / +Rx so one end of cable will be set TX and the other will be RX with respect to polarizing concept.
Router and PC have the same architect of cable ordering and their polarize so we will need to use cross (1-->3,2-->6,3 -->1,6-->2)in the absence of MDIX Technology

whenever there are devices working on the same layer of OSI model we will have to use  a cross over cable

so its the Layer of funtionality and nothing else..

becouse the both device have same  NIC  (when you send from PC Interface to router Interface the data will receved in send suction in the port)