Apple Mac Pro (Early 2008) - Manual (Page 47)

Chapter 3 Making a Good Thing Better 47
6 If you add a second pair of additional DIMMs, install them on the top memory card in
DIMM slots 3 and 4, the last two slots.
7 If you add a third pair of additional DIMMs, install them on the bottom memory card in
DIMM slots 3 and 4.
Second pair of
additional DIMMs Third pair of
additional DIMMs
Bottom memory card
Top memory card
2 3