Drive letter change confusion when adding 2nd hard drive, studying for A+ test.

[Scribels]

When studying for my A+ certification test, I run into this question:
http://www.simulationexams.com/SampleQuestions/a+dos_q4.htm

Q4. Your customer has bought a second hard disk and added it an existing computer. The first hard disk is having one primary partition and one Extended partition. The extended partition is divided into two logical drives D and E. When you install the second hard drive and format it, what would be the drive letter assigned to the first logical drive on the extended partition of first hard disk? Assume that the second hard disk has one primary partition and only one logical drive on the Extended partition.


I assume the answer is this:
1st drive: Primary partition = C - Primary, Extended partition = D and E

So when you add the 2nd drive you should get this:
2nd drive: Primary partition: F, Extended partition: G

So I would assume the answer is D

But the answer is really this:

The revised drive assignment looks as follows:

Drive 1: C (Primary Partition), E (First logical Drive), F (Second logical Drive)

Drive 2: D (Primary Partition), G( for Logical drive on Extended Partition)

Answer is E

What is the explanation for this? There is no explanation, that's just the answer. And the answer is E. There is no information explaining the change, why did it change and rearrange the volume label letters as such. Why wouldn't it just add down the alphabet? How am I suppose to know what Windows Operating Systems randomly do? Is there a special reason for what it did?

I googled drive letter assignment, and I'm not finding the explanation.

Why did it change D to E, and E to F? And why did it put D on drive 2?

 

[Phillip Corcoran]

Windows always assigns drive letters to primary partitions first. So if you install a second hard drive, it's primary partition will be assigned a drive letter that was previously assigned to one of the non-primary partitions on the first drive.

 

[Scribels]

Windows always assigns drive letters to primary partitions first. So if you install a second hard drive, it's primary partition will be assigned a drive letter that was previously assigned to one of the non-primary partitions on the first drive.

Thank you, now I understand how to get the right answer to this question. I'm am left wondering why it does it this way. Must be just the default order in which it does it.