Within the package Boot-US all partitions on a hard disk are assigned a partition number
according to the following rule:
For MBR partitions the primary and extended partitions are assigned always a partition number between 1 and 4.
Logical partitions are assigned always a partition number of 5 and higher.
Within each of the two groups the partitions are ordered according to their position on the hard disk.
For example a primary (or extended) partition with the number 1 lies before a partition with the number 2.
Similarly a logical partition with the number 5 always lies before a log. partition with the number 6.
For GPT partitions the protective partition is assigned the partition number 0.
The actual GPT partitions get a partition number starting with 1.
The numbers are based on the position on the disk. Higher numbers lie further back.