How do I install W10 on second SSD for dual boot system

I've found conflicting recommendations on whether it is necessary to unplug existing drives when installing Win 10 onto a second SSD. Desktop was drive 1 SSD (C:) and drive 2 HDD (D:) until I installed a second SSD to become (D:) so it will become:

1st drive > SSD (C:) with Win 7 on it.
2nd drive > SSD (D:) new/blank drive I'm newly installing Win 10 onto.
3rd drive > HDD (E:) with only data on it (never any OS).

Will install Win 10 from an iso on a CD. BIOS/UEFI (unsure of terminology) boot order was already set as:
#1 cd drive
#2 1st SSD (with Win 7)
#3 2nd SSD (new/blank) - I checked and it IS listed.

So, I'm trying to make sure I can dual boot AND the system is bootable even if one of the drives is removed at some point plus be sure that the drive letters assigned (as above) don't change. Another potential wrinkle is in disk management originally disk 0 was the SSD (with Win 7 on it) and disk 1 was the HDD (w/ no OS). After installing the new/2nd SSD (left SATA cable to 1st SSD as is was and just moved the other SATA cables down a notch so to speak) - but now it shows as new SSD as disk 0, original SSD as disk 1 and the HDD as disk 2. It is for sure connected to MoBo as: disk 0 = original SSD (w/ OS), disk 1 = new SSD, disk 2 = original HDD, disk 3 = CD drive.

Should I disconnect drives 1 and 3, then install Win 10 on drive 2 and reconnect other drives once Win10 after is up and working OR just leave all drives connected and install Win 10? If disconnect then from the MoBo end OR from the drive ends?
Thanks!

SIW2 said:

Your win 7 is bios boot, mbr partition style with the 100 mb system part flagged as active.

Are you planning on installing win10 using bios or efi? It will be simpler to use bios and mbr for that as well.

I'd forgotten about the mbr vs gpt issue. Idk enough about it to know for sure. From what I can tell mbr suits my situation. GA-Z77X-UD3H MoBo has GIGABYTE 3D BIOS (Dual UEFI) & I "think" UEFI is enabled. Whichever would work for both W7 & W10.

SIW2 said:

There is probably a setting that allows both, there is on gigabyte B75 mobos, which are similar.

Under BIOS FEATURES TAB.

WIndows 8 features, select Other OS

Boot Mode selection, select UEFI and BIOS

F10 to save and exit. You might already have those settings.

Mine is similar to your screenshot but doesn't list ANY OS option (where yours shows: "WIndows 8 features, select Other OS....") OR a "Boot Mode selection" to select UEFI and/or BIOS.


Further research finds a lot of instances where people have boot problems (either W7 &/or W10) even when they've disconnected the other drives and installed Win 10 on the unallocated drive. So, what I thought would be a fairly straightforward process adding another drive & OS apparently isn't!