I've really been struggling with this: I'm trying to install Windows 10 from Dell USB drive that I've made bootable, but it's only seen in the legacy options in the one-time boot menu. Secure boot is off and UEFI is enabled. I need the USB to be recognized as UEFI in order to install Windows to boot to UEFI. I'm using Rufus to make the bootable drive and I've tried both MBR and GPT partition scheme for UEFI with no luck. Is there any BIOS settings I need to check?
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The media must be at least 16 gigs and not larger than 32 gigs and USB 2.0.
This is why I recommend using USB 2.0 optical drive and OEM system builder DVD for reinstall.
It also means that ISO must be burned to DUAL Layer DVD media because the base installer is no longer smaller than 4.7 gigs.
Why the limit?
The 4 GB barrier is a hard limit of FAT32: the file system uses a 32-bit field to store the file size in bytes, and 2^32 bytes = 4 GB (actually, the real limit is 4 GB minus one byte, or 4,294,967,295 bytes, because you can have files of zero length). This means that you cannot copy a file that is larger than 4 GB to any plain-FAT volume. This means that past 1803 the WIM file is TOO LARGE for a FAT32 flash drive.
You can use exFAT or NTFS on newer models, however older systems are NOT able to boot from external boot media using NTFS.
For these models it cannot be exfat and larger than 32 gigs or usb 3.X drive.
The WIM file for WINDOWS 1809 and 1903 and 1909 are TOO LARGE for FAT32.
Thank you for the explanation and links, @speedstep I was finally able to create a bootable thumb drive with the Windows 10 1909 Pro ISO that my e7270 recognized!
However, after installing 1909, the BIOS/UEFI doesn't recognize the M.2 SATA SSD. It's flat out not visible in the configurations. Do you have any idea why this might be? I have tried updating the BIOS to the most recent, rolling back to earlier ones, and several in between, with no change. The M.2 box is checked as one of the drive types available. But in system configuration it's not listed.
I finally got it to work! I ran the Dell pre-boot system assessment, and the M.2 checked out OK. So I compared the boot sequence in this laptop to a known good one. I ended up having to manually add a boot option. So in case anyone else runs into this, in the BIOS/UEFI, under Settings\General\Boot Sequence, click Add Boot Option. Pick the File System List that includes, anywhere in that string, the Sata SSD (the Latitude e7270 M.2 is SATA, not PCIe). Click the ... to the right of File Name, and navigate to this: \EFI\Microsoft\Boot\bootmgfw.efi Give the boot option a name and click Ok. Pick the boot option you just created as the first in the boot sequence. Apply, and exit. It took extra long to boot up that first time, but I finally got the the initial Windows setup and it's working great!
PCI-E M2 Sata is not native to windows for many vendors. Fixing the BCD may also be required as may be safe mode and use of diskpart.
You have to install F6 mass storage Drivers aka PRE INSTALL drivers or it WILL NOT see the drive.
You CANNOT point to an EXE or ZIP or Cab file it must be extracted to the USB flash.
NVMe Driver Installation Guide
Newer versions of windows
INSTALL.WIM is larger than 4 gigs so it cant be copied to USB flash on 64 bit versions.
This was not an issue with 1803.
Media creation tool seems to do fine with FAT32 16 OR 32 GIG usb2 MAX
Force update now TO 2004
2004 media creation tool.
Just in case, you may not realize that your Flash Drive has to be formatted as FAT 32 in order to boot as UEFI..
It also has to be an x64 version of the OS.
I konw rufus, but it didn't work perproly, in many cases. There are may ISO burner tools on line you can choose, like wonderiso, unetbootin or RMPrepUSB.