If you have only one processor in IBM X Series Servers and you have two memory sticks to insert, the RAM population should be as follows.
Slot 3 and Slot 6
Slot 2 and Slot 8
Slot 5 and Slot 7
Slot 1 and Slot 4.
If you insert in other slots than the above mentioned, your server may not give the 100% performance as their mentioned configuration.
If you have three memory sticks to insert the order is as follows.
Slot 3, Slot 6 and Slot 8.