text: u can hav two processor in a pc but must be the same type. P3 using socket 370 but P4 using other socket like LGA 775 or others ... different socket different processor! Some processor but same kind can add into the motherboards to increase the speed but is limited to certain motherboard oni, and sometime its not stable... If u wan pc work faster, i reccomend u add RAM into ya PC. Remember, same kind of processor oni can b added into certain motherboard, and 1 processor at 1 motherboard !