What the heck just happened?

BIC · 11 Mar 2021

Five-year old Dell desktop with OEM Win10. Five-months ago, thought SSD C-drive was caput. After buying new SSD and installing Win10 on same, got the old SSD to work as an extra drive that wasn't being used. Things have been running fine until . . .

Yesterday, Windows Update automatically installed 2021-03 Cumulative Update for Win10 version update 20H2 for 64-bit (KB5000802). Build is 19042.867. Clicked update & shutdown.

This morning, PC was on with the new-install intro to Win10. I nervously clicked through setting up Win10 for the first time (not too nervous as I happened to do my weekly backup right before the update). Sure enough, apparently Win10 had re-installed itself. Back to Ground-Zero.

As I was trying to transfer data from external backup, said not enough room on C-drive. Something up there, as all this data had previously been on this 2TB SSD. As I perused hard-drive info (2 SSD and 1 HD), I saw the C-drive was on the old, small SSD. Should have been on the newer, large SSD.

I remembered I needed to disconnect all extra drives to install Windows. As I left only the newer, large SSD connected and started up . . . my trusty old Win10 installation with all my programs and data were there.

It appears that the Windows Update caused the PC to switch over to the old, unused SSD as the C-drive. I can't remember for sure if Windows was installed five-months ago or it was blank. Think I had installed Windows on there for troubleshooting purposes. I've now left the old SSD disconnected to avoid a repeat.

What the heck just happened? Thanks.

spunk · 11 Mar 2021

You answered your own question. You have 2 SSD drives with Windows 10 on them. The smaller older SSD should have been removed and put on the shelf for Troubleshooting purposes, or left unplugged. If it was still in the Boot order, even if it wasn't the first boot device, when Windows updated, it updated your old SSD instead of the newer SSD. If you want to keep it in the computer, then in the Bios/Boot tab, remove the old SSD from the Boot order, or move it down the list. Or wipe the drive and use it for storage. If you want to keep it for Troubleshooting, leave it unplugged or remove it from the computer all together.

Paul Black · 11 Mar 2021

Hello @BIC,

To Remove the additional Win 10 OS from the Bootloader Menu, have a look at this . . .

> How to Delete Boot Loader Entry on Boot Options Menu at Startup in Windows

To Change the display order in the Bootloader Menu, have a look at this . . .

> How to Change Display Order of Boot Loader Entries on Boot Options Menu at Startup in Windows

It is never a good idea to have two booting Win 10 systems because of such reasons relating to them and the BIOS. That is why when performing a Clean Install for example, that ALL other Disks are removed . . .

Disconnect ALL Other Disks

It is highly recommended that you disconnect [ temporarily unplug ] ALL other Disks [ HDD's/SSD's/USB's ] BEFORE installing Windows. The reasons for this are . . .

You CAN'T accidentally OVERWRITE a connected Disk.
The BOOTLOADER [ boot configuration files ] will get installed on the correct Disk [ because Windows has the tendency to install the bootloader rather randomly on ANY connected Disk ], and therefore STOP problems with booting once the installation is complete.

Once the installation is complete . . .

Check that the OS boots correctly.
Check if the boot order in the BIOS/UEFI settings are correct [ if NOT, adjust accordingly ].
Reconnectthe other Disks.

EXPLANATION:

Windows uses a different partition structure for BIOS/UEFI. During the installation process, Windows asks which Disk / Partition you want to use for the Windows C:\ drive, it does NOT however, necessarily use the same Disk for the other Partitions, and can therefore incorrectly create the hidden recovery partition on ANY attached Disk.

Additionally, for BIOS, if another Disk is left attached, and at a latter stage you remove that Disk, you will find that the OS will NOT boot. If you check the BIOS, you will see that the OS has assigned the AHCI/RAID setting instead of the LEGACY setting and set it up as RAID, therefore breaking the boot process.

I hope this helps.