Why does the letter of the system partition change after connecting the card reader?

Question

Windows

To increase the speed of the computer, I installed the Windows 10 system on an SSD drive, leaving the old hdd for storing files. During Windows installation, the hdd was disabled. After connecting the hdd, an inaccessible boot device error occurred. The diskpart program showed that the partition on the hdd disk had the partition letter changed to C:\. The partition letter on the ssd became D:\. After disabling hdd, the letter C: \ returned to the ssd partition of the disk and the system booted successfully. The disk priority was set correctly, first ssd, then hdd. SSD is connected to SATA-0 port, hdd to SATA-1. The partition on the hdd disk is logical. I changed the partition letters in the diskpart program. After the reboot, the letters of the partitions were returned incorrect. I also changed the letters in the acronis disc director program, it did not help. And only after turning off the card reader, the system booted up with ssd and hdd disks. The card reader is displayed in the system with four letters. A card reader is needed, there are two usb ports, an hdd is also needed, all information is stored there.

Answer 1

Why does the letter of the system partition change after connecting the card reader? It can not be.

During Windows installation, the hdd was disabled. After connecting the hdd, an inaccessible boot device error occurred.

There is probably an active partition on the HDD and the download was transferred to it.
The drive letter has nothing to do with it.

The diskpart program showed that the partition on the hdd disk had the partition letter changed to C:\

Where was this program launched? This program runs on the operating system.
And it is the operating system that mounts partitions on some letters, or does not mount.

After the reboot, the letters of the partitions were returned incorrect.

During the boot process, the system mounts disks - assigns letter identifiers to partitions.
The partition on which the system itself is located is assigned the letter C: |, the rest as it turns out.
If you installed the system without removing the old one, the new one can be installed on a different letter - for example, on D, or on X, and then at each boot, this system will assign this letter to the partition where it is located, and the rest of the partitions - how to get, alphabetically, from unoccupied letters.
The letter on which the partition is mounted does not affect the boot in any way, because at the boot stage it is not known what letter this partition will be mounted on!

Answer 2

1 - loading occurs from a physical disk that is selected as a priority in the BIOS
2 - letters to the bootloader up to the lantern
3 - letters are assigned in the registry of the bootable system (see screenshot https://i.imgur.com/vmrtZ23.png)
so you either then you confuse, or look for an insidious virus - in the sense that you are not loading what you expect
ps
note - acronis changes letters for itself, nothing more,
check the card reader for a bootable flash drive / card

Answer 3

The disk priority was set correctly, first ssd, then hdd. SSD is connected to SATA-0 port, hdd to SATA-1.

Many BIOSes have two priority lists - a list of all disks, and a separate list of boot disks. If you set the order of disks in the first list, but forget about the second, then it will be like yours, since the first list does not matter for the boot order. It also doesn't matter what SATA plugs you plug the drive cables into.

for a partition on a hdd disk, the partition letter has changed to C:\. The partition letter on the ssd became D:\. After disabling hdd, the letter C: \ returned to the ssd partition of the disk and the system booted successfully.
... I also changed the letters in the acronis disc director program, it did not help.

The OS sets the order of the letters as it wants. If you need to change it and fix these changes permanently, then you need to do this using the OS tools - the Disk Management tool. But even then, for example, when installing a second OS, it will set its own order of letters, and it must also be configured using the means of this second OS.
The boot is completely independent of what letter order you have assigned, it is determined only in the BIOS.

The partition on the hdd disk is logical.

Here is more detailed. The fact is that there cannot be one logical disk. In order for a logical disk to appear, you must first add an additional one to the main partition of the disk, and already make logical ones in it. I am hinting that in addition to this logical partition of yours on the disk, the main one is hiding somewhere from your eyes (it is most likely active at the same time, i.e. bootable), and this well explains some of the nuances you described.

The card reader is displayed in the system with four letters.

Yes, those "4 in 1" card readers are usually displayed in the OS like that, even when nothing is inserted into their slots. If you want this not to happen, replace it with a regular USB hub, without card reader options.

Answer 4

The reason turned out to be a dvd drive connected with an ide cable.