Apple Mac Pro (Mid 2010) - Manual (Page 58)

58 Chapter 3 Making a Good Thing Better
If you install equal-size DIMMs (for example, all 1 GB DIMMS or all 2 GB DIMMS) in your
8-core or 12-core Mac Pro, Apple recommends that you fill the slots in the order listed
in the table.
Slot 4
Slot 3
Slot 2
Slot 1
Slot 5
Slot 6
Slot 7
Slot 8
If you have Fill these slots
Two DIMMs 1 and 2
Three DIMMs 1, 2, and 3
Four DIMMs 1, 2, and 5, 6
Six DIMMs 1, 2, 3, and 5, 6, 7
Eight DIMMs 1, 2, 3, 4, and 5, 6, 7, 8 (all)