What decides a volume number

Running Windows 10 20H2 on two PCs.
I am puzzled by the definitions displayed by diskpart list volume.
I attach the two displayed contents of 'list volume'.

It is mainly the first of these that I am puzzled by. Both machines are, as far as I can tell, cabled the same way but give very different results.
The first machine (ALANPCS8) has recently had to be rebuilt as it suffered a irrecoverable error. I did not change the cabling internally. The drives with a size 3725/6 are 4TB HDD mounted on an externally accessible location on the case.

Can anyone tell me how the volume numbers come to be so different? or point me to documentation which might help?

The operating system (Windows) decides the volume numbers. It depends a lot upon in which order additional partitions are created after Windows is installed. The top computer in your screenshot has one more partition than the bottom partition - probably an extra recovery partition.

The extra partition pointed out by NavyLCDR is a 513MB hidden partition which as Navy says is a recovery partition. Generally Windows will add additional recovery partitions during a version upgrade. You say that one of the images comes from a PC that has recently been rebuilt. Might that be the one with the extra partition? If yes might Windows have been version upgraded during the rebuild?

Ghot said:

@MacNala

What does list disk show?

Thanks for the interest here are the answers
diskpart7.txt
diskpart8.txt

Does that provide any more explanations.

You need to understand the difference between disks, and volumes/partitions. Disks are assigned numbers based on what physical port on the motherboard they are connected to. Motherboard ports are numbered starting with 0 and advance upward. In your case with 3 physical disks you have disk 0,1,and 2.

Partitions
Storage media (DVD's, USB sticks, HDD's, SSD's) can all be divided into partitions, these partitions are identified by a partition table.

The partition table is where the partition information is stored, the information stored within here is basically where the partition starts and where it finishes on the disc platter.

Volumes
A Volume is a logical abstraction from physical storage. Large disks can be partitioned into multiple logical volumes.

Volumes are divided up into fixed size blocks or a cluster or blocks.

We don't see the partition as this is sorted by the file system controller but we see volumes as they are logical and are provided by a gui with a hierarchical structure and human interface. When we request to see a file it runs through a specific order to view that information from within the volume on the partition:

A Partition is limited to a single disk.
A Disk may contain one or multiple partitions.
A Volume may span multiple disks as there are several types of Volume:

Railtech said:

You need to understand the difference between disks, and volumes/partitions. Disks are assigned numbers based on what physical port on the motherboard they are connected to. Motherboard ports are numbered starting with 0 and advance upward. In your case with 3 physical disks you have disk 0,1,and 2.

Rest of post deleted as irrelevant to problem.
Both machines have ports 0 and 1 connected to HDDs in a Mirror RAID manner.
The HDD of size 3725/6 is externally connected to the interface from the motherboard. I have used another piece of detection software ReadSpeed from Steve Gibson of SpinRite fame.
From this I can see the ports to which the HDDs are connected and I have found that contrary to my previous understanding the externally connectable HDD on ALANPCS8 is on a different port from the machine named ALANPCS7.
I attach the output from this detection software. The first being from alanpcs7 and the second from alanpcs8
while this does not answer my original question it explains why I was getting confused.
The drive needs changed to the same port, which I will do when I have more time.