Unable To Boot In Legacy Mode

I believe you'll find that's by design.  Since legacy versions of Windows are no longer supported by CPUs in current generation systems like this one, and since most newer versions of Linux are UEFI-compliant -- there's not much if any need to boot the system in legacy mode (from the internal drive) any longer.

Eventually, legacy mode will disappear entirely - that's on Intel and Microsoft's roadmap -- this is just the next step toward that.

The reason the option is called "Legacy External" is because Latitude xx90 devices only support booting external devices in Legacy mode.  Internal devices need to be booted in UEFI mode.  I don't know why this change was made, but the bottom line is that you'll need to deploy a UEFI-compatible image to these systems, which depending on your imaging solution might also creating bootable media that supports UEFI mode as well, since some installation routines decide whether to lay down a Windows image in BIOS or UEFI mode based on how the image installation environment itself was booted.

This would be the "why".  Intel will kill off legacy boot by 2020.

https://arstechnica.com/gadgets/2017/11/intel-to-kill-off-the-last-vestiges-of-the-ancient-pc-bios-by-2020/

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@ejn63wrote:

This would be the "why".  Intel will kill off legacy boot by 2020.

https://arstechnica.com/gadgets/2017/11/intel-to-kill-off-the-last-vestiges-of-the-ancient-pc-bios-by-2020/

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I know, but I admit it's odd to support Legacy boot but only for external devices, especially since as I mentioned above, if you boot regular Windows Setup media in Legacy mode, it will install Windows on the drive in Legacy mode even though that would not be bootable on this particular system, leading to this exact confusing result.  Maybe there are some external diagnostic tools that don't yet support UEFI but that some customers still need to use.

LEGACY Booting is no longer supported past SKYLAKE.

32 BIT OS and Drivers are no longer supported by anyone.

64 BIT windows 10 or Linux in UEFI mode is the only thing supported going forward.

This means ancient Linux that uses GRUB/MSDOS MBR booting is also not supported.

CSM with MBR legacy booting is gone as is support for windows 7.

The good news is that the Current UBUNTU works on current systems as well as ancient ones.

http://releases.ubuntu.com/18.04/ubuntu-18.04.2-desktop-amd64.iso

I installed this recently on a 2006 Optiplex GX620 alongside windows 10 and it worked fine with both OS.

I would not recommend any systems prior to 2006 however as they do not support 4 gigs of ram or more and do not support 64 bit LAHF SAHF , NX , CMPXCG 128 etc so 64 bit windows 10 wont run on these systems.

Optiplex GX390 GX620, 745, 755, 760, 780, 790, 960, 980,990 all work fine from MSDOS all the way thru Windows 10.

3010 3020 7010 7020 9010 9020 also work fine. These are the last units that will boot and RUN XP.

Newer Systems should stick with Windows 10

DELL has Cab files with all of the Drivers for these units.

https://www.dell.com/support/article/us/en/19/sln312414/dell-command-deploy-driver-packs-for-enterprise-client-os-deployment?lang=en

Not supported does not mean not working with windows 7 or 8 or 10.

Here is the fix everyone: Format your USB flash drive in FAT32, mark it Active and then boot it in UEFI.

My laptop was 3 months old when I tried to do a clean installation of Windows and was stuck with no bootable devices message. I contacted Dell for almost 2 hours, went through two techs on the phone, and then their supervisor, found out that my warranty was just "basic" and they couldn't help me with anything further if I don't purchase one of their "premium" packages. That was a lot of help and understanding there Dell employees!

I then tried to keep searching on how to boot from USB devices in UEFI mode and apparently FAT32 is the "format" that the UEFI system can recognize so I went on with my installation from there. Hope this will help someone.

@donglacville  that's correct.  FAT32 support is mandatory in the UEFI spec, so that's what you should use.  NTFS support is optional and not very widely implemented, so typically flash drives formatted NTFS will only be bootable in Legacy mode, which can result in a Legacy mode installation of Windows that would be unbootable on a Latitude xx90 system.  The issue with FAT32 is that it doesn't support files larger than 4GB, which can make packaging some system deployment images a bit difficult, but depending on the tools you use and whether you're using the flash drive to store the image itself or just to boot the system and then pull an image over the network, that can typically be worked around.

So does this explain why there appears to be no option in my (very new) Inspiron I5 7590 laptop UEFI setup to 'enable legacy rom'? The text associated with the setup - rather embarrassingly, I believe - refers to 'enabling legacy ROM option' but that is nowhere to be found. The only option appears to be 'enable UEFI network stack'. I have an (also new!) Asus Zen USB2 DVD R/W drive plugged in which is readily available in Windows, but I'm completely unable to see it as a boot option. I have a CD that would normally boot into a CD version of Windows and enable a disk image to be created using O&O DiskImage software - but there's no way I can get it to boot. Any comments are very welcome! Thanks - Mike

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@Mikeinnc wrote:

So does this explain why there appears to be no option in my (very new) Inspiron I5 7590 laptop UEFI setup to 'enable legacy rom'? The text associated with the setup - rather embarrassingly, I believe - refers to 'enabling legacy ROM option' but that is nowhere to be found. The only option appears to be 'enable UEFI network stack'. I have an (also new!) Asus Zen USB2 DVD R/W drive plugged in which is readily available in Windows, but I'm completely unable to see it as a boot option. I have a CD that would normally boot into a CD version of Windows and enable a disk image to be created using O&O DiskImage software - but there's no way I can get it to boot. Any comments are very welcome! Thanks - Mike

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@Mikeinnc  if you don't see a way to switch between UEFI mode and Legacy mode or an option to enable Legacy Option ROMs, then your system might not support Legacy booting at all.  I haven't used that system personally though, so I can't be certain.  Another possibility I suppose is that if you disable Secure Boot (which you can't use with Legacy mode), then Legacy Option ROM support is automatically enabled even if it's not shown anywhere.

As for booting from an external drive, lack of Legacy support wouldn't explain the drive missing from the boot list entirely because it's possible to boot from optical drives in UEFI mode.  However, sometimes being able to boot from external optical drives and especially external network adapters requires that the system have firmware-level support for that specific external device to use it at boot.  If that isn't feasible, given that optical drives have been disappearing from laptops for a while now, you might want to see whether you can get a USB flash drive version of whatever tool you're currently booting from a CD.  You could probably even capture that CD as an ISO file and then use that ISO to generate a bootable flash drive.  There are various free tools to accomplish each of those tasks.  Or if you're just looking for a solid disk imaging tool, take a look at Macrium Reflect.  It's a popular imaging/cloning solution here and elsewhere because the free version for many people has everything they need, but for people who perform imaging on a regular basis, the paid version has some nice features.

@jphughanThanks so much for your prompt reply. I believe I have to concur with you - it looks like Legacy booting has been removed. We can't say we weren't warned! I had tried disabling 'secure boot' when I wrote my original post, but there is no evidence at all that it enables any 'hidden' legacy boot process. I also understand what you are suggesting re optical drives. When I bought this computer, I knew it came without an optical drive, but I'd always intended to buy an external USB DVD drive as I still have quite a few optical disks. I guess I'd assumed that I'd also be able to boot from it - looks like I may have got that one wrong! I'd already considered "converting" a bootable CD into a USB flash drive, and it looks like that might be the only option. I know I can, in fact, boot from a USB flash drive - I've tried it and it works (although not with the Windows PE / O&O Diskimage combination). I guess I was still half-hoping that someone 'out there' might have known the 'open sesame' for booting from the DVD. Looks like I got that one wrong! Thanks again for you help - and I'll certainly have a look at Macrium Reflect as you suggest.

@Mikeinnc  happy to help!  I too bought a USB optical drive.  I decided to spring for a Pioneer Ultra HD (4K) Blu-ray drive figuring that it would probably be the last optical drive I ever bought since I'm not even sure movies will be distributed on physical discs for another generation.  But I didn't expect I'd be able to boot from it, and ever since I saw how much faster things boot and load from USB compared to disc, I haven't really wanted to boot from a disc anyway.  That's especially true for installing Windows, which occurs SO much faster from even a half-decent USB 3.0 drive than it does from a DVD.

That said, I'm surprised Legacy booting is already gone.  Intel did say that their CPUs would stop supporting Legacy booting in I think 2020, and the Latitude xx90 models and newer now only support Legacy booting from external devices, but this is the first I've heard of Legacy booting being removed entirely.  Then again, maybe it makes sense, because there are several threads from Latitude xx90 owners/administrators wondering why they can boot their systems into their image deployment environment but then can't boot the imaged hard drive.  The answer is that they were booting the imaging environment in Legacy mode, which caused it to install Windows in Legacy mode, which isn't possible to boot on those systems.  The fix is to boot the imaging environment in UEFI mode so Windows installs itself in UEFI mode, which has quite a few advantages anyway (including Secure Boot), so perhaps Dell decided that "partial" Legacy support was more trouble than it was worth.  I think the original thinking for it was that people might have certain diagnostic/recovery/specialty tools that they'd occasionally need to boot into and that don't support UEFI mode, but considering that UEFI mode has been widely supported on systems for more than 5 years now, lack of Legacy support shouldn't be too much of an inconvenience at this stage.

@jphughanWell, looks like we may both have been fooled! After our previous conversations, I managed to use a more up-to-date version of the program that allows you to build a bootable disc image using the Microsoft Windows Assessment and Deployment kit. And, having done that and burnt it to a CD-R, with the DVD drive plugged in - voila! When I rebooted and hit , there was the USB DVD drive as a bootable option! No 'legacy' issues to change - just select and a few minutes later (and, yes, it really did take minutes!), a running system as expected. Now clearly, that disc had been built using UEFI processes, and maybe that was the real issue? It wasn't that I couldn't boot from the drive itself - more that the original non-UEFI disc that was in the drive obviously wasn't recognised. So at least we know it is possible! However, I still believe that your preferred option of a USB flash drive is the better one. And, yes, I tried that too with a saved ISO image from the build, and, of course, it worked perfectly. Thanks for all your kind advice and help - hope this gives you some more food for thought. Regards - Mike

when creating a USB flash drive for UEFI do both EFI and OS install partition have to be in FAT32 or just the EFI partition?