fsb is the front side bus... basically.. the higher the number the faster, dual RAM is better than single, Dell compares it pretty well... single channel RAM is like a 4 lane highway, Dual channel RAM is like an 8 lane highway.. and stay in the same range if u run dual... dont put PC2700 and a PC3200 together.. its best to just exchange the PC2700 for a PC3200!! most people stick with 2 sticks of 512MB PC3200