It's possible Windows installed its bootloader and boot partition onto the drive you removed.
Assuming the rest of your system is on the drive you didn't swap out, you can try copying the Windows boot sector byte for byte from the swapped out disk to a partition on the new disk. Make sure to also set the necessary partition flags. Then you can probably boot a Windows installer and use the common boot fixes (fixboot.exe and friends).
Assuming you have a modern Windows system, you also need to make sure the UEFI partition (a FAT32 partition that contains a file path something like /EFI/grub/grubx64.efi
) also contains the Windows bootloader.
On a single disk you would end up with something like this:
Disk name | Partition 1 | Partition 2 | Partition 3 |
---|---|---|---|
/dev/disk/by-diskseq/1 | UEFI (a few GB, FAT32) | Windows partition (hundreds of GBs) | Windows boot partition (±300MB) |
/dev/disk/by-diskseq/2 | Linux boot partition (1-2GB) | Linux swap partition (same size as your RAM) | Linux partition (hundreds of GBs) |
Your Linux layout will depend on your settings. If you use LVM, all partitions are probably virtual partitions within one large partition. One or more may be wrapped inside an encrypted partition as well.