BIOS vs. UEFI
In the past there was only BIOS, but in recent times UEFI and EFI have become the new standard for motherboards to use. The main reason for this is that BIOS has space constraints that UEFI improves upon. Much like many protocols, BIOS was made and meant for a certain era, while UEFI attempts to modernize and supplant BIOS.
The simplest way to think of UEFI is like a better BIOS.
Multi-UEFI (GPT) Bootable USB
I want to start off stating that Linux and Unix users have had the capability to use a multi-UEFI bootable USB's for quite some time, albeit through a CLI (Command Line Interface). But Windows users have really not had the ability to do this--until now...
Why is a multi-UEFI bootable USB a good thing? Because you may have several rescue CD's or Windows/Linux Live CD's that you want on one USB as opposed to several. For example, if you were IT for a company that fixed systems, it would be a big hassle to use several USB's, and even worse if none were labeled!
Is It Necessary To Use UEFI?
I would argue that currently it is unnecessary. I have never come across a motherboard for either a desktop or laptop that primarily used UEFI (or EFI), but did not have a "legacy" mode that would allow for a BIOS-compatibility mode.
In essence, this is a switch to change between BIOS or UEFI.
That being said, it should be noted that it is likely that this will not always be the case. It may take a long period, but I doubt that this legacy mode will always be around. And, for the sake of simplicity, it is much nicer to be able to just plug in a USB and not fiddle around with UEFI settings beforehand to get a USB to be recognized.
While having to switch a couple of settings does not sound like a chore, it certainly can be. Last week I had to do a lot of testing in legacy mode; so I had to go into the UEFI, switch to legacy mode, test a USB, go back into the UEFI, switch back to UEFI mode, then restart to get back to Windows. It was not fun.
Some of you may already know of YUMI, it is most commonly known as a multi-boot USB for BIOS (MBR) systems. It is simple to use, portable, and has an intuitive interface.
What most people may not know is that YUMI now offers a UEFI beta version of their program. This only works with 64-bit systems, so be aware that any 32-bit system will not be able to utilize this version of YUMI. (A 32-bit version is being worked on). You must also disable Secure Boot if it is enabled in your UEFI.
There are a few (known) restricted rescue CD's and Live CD's that will not work with YUMI UEFI, which is not something the YUMI creators can fix.* That is because these CD's were not made to work with UEFI, so support for this CD's would have to come from the CD creators.
And while there is a list in YUMI of CD's that can be used, CD's that are not on the list are not guaranteed to work or not work. You will have to try such CD's to find out if they can boot and work properly.
*In this list, CD's that cannot work in UEFI will have a note next to the name stating "BIOS ONLY".
Using YUMI UEFI is very simple, but I will outline the steps for those who would rather get a sense of what to do first:
Go to the YUMI homepage.
Scroll down to "Beta Download -> UEFI YUMI - Windows".
Download YUMI UEFI by clicking on the "UEFI YUMI - Windows" text only.
Double-click the "UEFI-YUMI-BETA-0.0.0.#.exe".
Press "I agree".
Click the dropdown arrow under "Step 1".
Select the USB flash drive you have inserted.*
Click the dropdown arrow under "Step 2". This will show you a menu of every known rescue and Live CD that YUMI supports.
If you do not have one already, download a rescue or Live CD you wish to use.
Click the dropdown arrow under "Step 2" again.
Select the rescue or Live CD you have ready. If your rescue or Live CD is not in the supported list, you can either choose a supported rescue or Live CD that from the list that may be similar so you can move onto "Step 3".
Press "Browse" under "Show All ISOs?". Check off "Show All ISOs?" if your rescue or Live CD is unsupported, or if you have changed the original name.
Browse for your ISO and double-click it.
Check off "Format #: Drive (Erase Content?)".
YUMI will not show a progress bar, and when full, it will display a "Finished" button. Click "Finished".
*Note I: If you do not have a USB flash drive inserted, do so now, or check off "Show All Drives?", then select any drive. But be careful, you do not want to accidentally format your OS drive.
Note II: An external USB HDD/SSD (and in fact an installed HDD/SSD) can also be used to create a Multi-UEFI bootable device. To find these options, check off "Show All Drives?" in YUMI.
To test your multi-UEFI bootable USB, first ensure that Secure Boot is disabled in your UEFI. Reboot your computer and click the F# key to get to your Boot Priority screen (or go into your UEFI and either rearrange for USB devices to be found first, or select the USB to boot from it). If the multi-UEFI USB is working, the Boot Priority screen will just show a USB, instead of a designated name that you might find using a BIOS.
While in theory this should work with any USB and USB port, I would recommend using a USB 2.0 flash drive, however, a USB 3.0 flash drive may work fine. But even moreso, be sure to test on a USB 2.0 port, if possible.
The reason I mention this is because I have found USB 3.0 ports to be finicky at times, especially during POST. I did not have this problem with my multi-UEFI bootable USB, but I tested with a USB 2.0 flash drive in a USB 2.0 port...
No, it really is that simple. There are a few useful rescue CD's that cannot be booted from UEFI, but the majority you may know of are all available for UEFI.
For someone like me who may need to diagnose or repair a UEFI system every-so-often, a multi-UEFI is worth its weight in gold! And I know that more than a few people have been waiting for an easy method to make a multi-UEFI from Windows.