How do I use Legacy Boot

[donaldgary1]

I want to be able to use Legacy Bios so that I can boot from a variety of devices with a variety of unsigned operating systems.  How do I do it?  (I've read a lot of answers to this question, but none of them seem to work on this machine.)

[Lil_Boy_Blue]

Hi

Dunno really.

If you put a Linux on a secure boot disk then a coupla things could happen...

You get an MBR area of a few hundred megabytes to accept non-secure OS's.

AND/OR you can add a Secure Key to the Main Board to sit alongside Microsofts.

Could TPM and / or BitLocker get in the way?

Shim and MoK Manager may help.

https://www.aioboot.com/en/secure-boot/

https://www.rodsbooks.com/efi-bootloaders/secureboot.html

Or just have a second hard disk fitted.

[donaldgary1]

I was clearly too brief.  Let me add some background.

On my old desktop I had a VERY robust backup system.  I did NOT have any internal disk storage.  Instead I had two front panel drive slots for  2.75" SSD's.  I used one slot for  a 250 GB SSD that had the OS and all my data.  I used the other slot to make disk image backups using Acronis.  When I made a copy it became the new working disk and I saved the old disk as a the backup.  In this way I always knew that my backup would work.  (There's no joy like finding out your backup doesn't work when you need it.)   If I got a virus, installed software that was hard to uninstall, or did anything else that I wanted to undo I simply rebooted from the backup disk and made a new copy.  This easy recovery saved me more times than I care to count.  Occaisionally from viruses but more often from my own foolishness.  Almost as important,  it allowed me to try things I would never have tried otherwise since the worst case disaster was that I would have to reboot using a backup disk.  Before my old machine died I had seperate SSD's for Windows 7, Windows 10, and recently Linux.  

I really love this system and don't want to abandon it.  (If necessary I will give away this  useless and now-hated HP tower and build my own machine.  The machine is simply not worth another 10 or 20 hours trying to make it work.) 

My ideal endpoint would be to remove or disable the internal SSD and boot from swapable SSD's as before.  (The presales support at B&H Camers assured me I could do this.  In retrospect I should have known someone doing presales support is unlikely to actuall know anything at this level. )   

Is there anyone who can provide fairly detailed information on how to make this work?