Normally the HD in the lowest numbered SATA port is Disk 0, 2nd lowest is Disk 1 and so on .... I have experienced shifting but this usually works.
Two thing you may want to do as you add drives is this:
1. Change all the drive letters and then change back. Windows assigns letters in a default order that kit sees them, as you add drives, these change. If you change it, then Windows remembers and keeps this assignment.So ...
a) Change your optical, if you have one, to Z:\
b) Change D:\ to Y:\ and then back to D:\ .... now it is forever D:\
c) Rinse and reapeat with other drive partitions
2. Put your assigned drive latter as part of the partition label. For example:
(C: ) => C-Boot (C: )
others (D: ) = > D-Others (D: )
The advantage of this is that:
-If windows reorders the drive letters when you install a new drive you will be able to recognize C: as your "Boot" partition.
-All the drives will appear in order in top half of Disk Management
-When you add new drives, windows won't reorder