Install Windows 10 LTS without extra partitions

BIOS systems with MBR require only one NTFS partition to boot Windows.

UEFI systems with GPT requires two. A FAT(32) system partition for EFI boot files and a NTFS partition for Windows.

First make a bootable USB drive of the latest LTS Windows. Then boot and press shift-F10 when the installer loads to start the command prompt.

The instructions for an UEFI system (GPT):

diskpart
sel dis 0
cle
con gpt
cre par efi size=31
for quick fs=fat
ass letter=s
cre par pri
for quick
ass
exi
cd /d d:\sources
dism /apply-image /imagefile:install.wim /index:1 /compact /applydir:c:\
bcdboot c:\windows /s s: /f uefi
exit

Then exit the installer and boot into your new two-partition Windows installation.

Smallest possible EFI partition size seems to be around 36 MB for FAT32 and 25 MB for FAT(16) to fit all the boot files (only 4.5 MB if files are trimmed to minimum). Diskpart automatically aligns the created partitions to 1 MB boundaries. The image is applied in compressed compact mode and the Windows Recovery Environment is automatically installed to C:\Recovery\WindowsRE\Winre.wim.

The instructions for a legacy BIOS system (MBR):

diskpart
sel dis 0
cle
cre par pri
act
for quick
ass
exi
cd /d d:\sources
dism /apply-image /imagefile:install.wim /index:1 /compact /applydir:c:\
bcdboot c:\windows /s c: /f bios
exit

Then exit the installer and boot into your new one-partition Windows installation.

When using a NVMe SSD enable the faster Direct Access Storage mode with format /DAX c:.

The best of both worlds is to use MBR with EFI system partition. This setup allows booting with both BIOS and UEFI modes:

diskpart
sel dis 0
cle
cre par pri size=63
act
for quick fs=fat32
ass letter=s
cre par pri
for quick
ass
exi
cd /d d:\sources
dism /apply-image /imagefile:install.wim /index:1 /compact /applydir:c:\
bcdboot c:\windows /s s: /f all
diskpart
sel dis 0
sel par 1
set id=ef
exi
exit

Then exit the installer and boot into your new MBR-EFI Windows installation.

How to split Windows 10 installer to FAT32 and NTFS partitions (bootfiles and wimfiles) allowing larger than 4 GiB install.wim/esd on UEFI systems as UEFI needs a FAT partition to boot

copy boot.sdi to \sources
edit \boot\bcd and \efi\microsoft\boot\bcd
bcdedit /store bcd {default} device ramdisk=[C:]\sources\boot.wim,{ramdiskoptions}
bcdedit /store bcd {default} oadevice ramdisk=[C:]\sources\boot.wim,{ramdiskoptions}
bcdedit /store bcd /set {ramdiskoptions} ramdisksdidevice partition=C:
bcdedit /store bcd /set {ramdiskoptions} ramdisksdipath \sources\boot.sdi

docs.microsoft.com