What is the differance, personell wise, between the 3-4 and the 4-3 defense

Well to run the 3-4 you have to have 4 good LB'ers(Swilling, Mills, Jackson, Johnson)....and 3 down linemen that can get pressure on the QB in case you want to use the 1 or 2 of the ILB'ers in coverage. Yeah back in the day we did have 4 great LB'ers :)