i bought a hp pavilion 15 note book laptop . I have bin using it for last 2 months i am only having 4 gb ddr3L RAM so the system is getting slow when i open 3 or 4 windows at the same time. i am planing to add 8 gb more of ram can i use different manufactures like kingston and transcent same time or should i get rid of the old 4gb ram and buy same manufacture my LAPTOP can only support 12 gb ddr3L ram so i have buy one 8 gb and one 4 gb ram.