An odd quirk of disk numbering in Windows

[mikeymikec]

I'm working on a customer's Lenovo AIO PC, doing a clean install of Win10 on it. It has an SSD and a HDD in it, with Windows installed on the SSD. Oddly though, the old install of Windows numbered the SSD as disk 1 and the HDD as disk 0.

Initially I was going to disconnect the HDD for the OS install as part of the usual best practice (mainly to ensure that nothing OS-wise ends up going on the HDD). After reading up on how to take the PC apart, I decided against it (elements like undoing the plastic clips around the screen made me feel that there was an element of risk such as damaging the chassis in a visible spot), feeling that the risks though small likely outweighed the benefits.

I had already backed up all the likely useful data from both drives anyway and if weird stuff occurred as a result of the HDD being connected during setup time, I could always go back to my initial plan.

So, I booted from my Win10 setup USB stick and was surprised to find that the SSD was labelled disk 0! Cool. I nuked the partition structure from the SSD and left the HDD's single partition intact. Windows then finishes installing, and on logging in I find... the SSD is disk 1 again.

Wut.

 

[Steltek]

I presume the SSD is a SATA SSD?

Did you try disabling detection of the HDD in the BIOS before partitioning, formatting and installing Windows on the SSD?

 

[pcgeek11]

HDD is plugged into port 0 and SSD is plugged into port 1. Swap them if you want it to change.

It is however a none issue.

 

[Steltek]

HDD is plugged into port 0 and SSD is plugged int port 1. Swap them if you want it to change.

It is however a none issue.

I don't know if Win10 works like Vista through Win8 did, but those prior Windows OSes enumerated disks though a separate process from the BIOS. That process sometimes resulted in disks being assigned differently in storage manager. There was a KB issued by Microsoft several years ago (don't remember the number) recognizing that it was happening.

In fact, my old i3770k machine has this exact issue. Windows 7 is installed on DISK1 despite fact that the current OS disk is plugged in to SATA port 0. I can tell you from experience that it is impossible to get Windows installed on DISK0 on that machine unless you install it specifically on a hard disk plugged into SATA port 3, and even then it isn't always a sure thing.

However, like @pcgeek11 points out, it is really a non-issue that for all intents and purposes results in no functional problems with the machine. It is certainly not worth wasting any effort to fix it.

 

[mv2devnull]

OS (and BIOS) are quite free to enumerate and name devices as they please. (I had VM with multiple NICs and their order/names did change on every boot.)

Disks have serial numbers. Partitions and filesystems have UUID (in the disk).
UEFI finds filesystem marked "EFI System Partition" and (attempts to) loads bootloader from it.
Bootloader's config has UUID of OS filesystem. It can locate that filesystem to load the OS.
In Windows, when you assign specific drive letter, an UUID <-> letter is stored somehow.
(Cloning or breaking mirror creates two filesystems with identical UUID. Not fun.)