Scenario: After booting from one of our recovery media you see that the drive letters are different than in Windows.
In the installed Windows the drive letters are usually entered to the registry database. The system drive gets the letter C:. A possible MSR (MSR = Microsoft System Reserved) partition does not get a letter at all for security reasons. Other partitions on internal disks get their drive letter by the order of their creation. Once fixed in the registry these letters are applied the same way on any Windows start.
When booting from one of the rescue media the letters can be distributed completely different.
The reason is, that another operation system (Linux or WinPE) is booted. This OS does not read the Windows registry and applies the drive letters by himself. It starts with C: (A: and B: are traditionally reserved for floppy drives) for the first partition on the first disk (disk 0), D: for the second one and so forth. This is nothing to worry about though.
Our software identifies a partition or disk not by the letters but by partition/disk numbers or IDs – anyway unique identifiers. Thus for example there will be no chance of failure when restoring a partition even if the displayed drive letter is completely different from the source.
Note: Drive X: will always be the mounted RAM disk. Thus X:\Windows will be the Windows directory of the running WinPE.