@cazabon yeah, Wubi from Ubuntu used to do that. I used it for a while back in the day. It's not going to bypass Secure Boot, though (which it seems Foone's Surface doesn't allow disabling) – and it had zero support for UEFI style boot in general – Wubi would just install grub4dos and configure it to be chain-loaded specifically from WinXP's NTLDR.(I don't think it touched the MBR? nor the VBR? I don't remember for sure, but I *think* it was ntldr->grub4dos specifically to reduce the chance of failure. Traditional dualboot would go rearranging things to do grub->ntldr instead, but Wubi was for a very non-technical audience.)These days as far as I know Windows's BOOTMGR refuses to boot anything that isn't digitally signed as a Windows component (unlike NTLDR in WinXP where you could still add arbitrary entries), so you can no longer chain bootmgr->grub, have to boot directly into grub from the beginning.imo, installing GRUB "from the outside" has become *kinda easier* in EFI world; the equivalent of "fiddling the MBR" on UEFI systems would be "fondling the EFI boot variables", which Windows has an API for (and you can do it through bcdedit, etc) – the bootloader lives on a FAT partition, drop grub.efi in there, add a new boot entry that points to grub.efi – but of course that grub.efi isn't "Microsoft-signed" so it still won't boot no matter what.as I understand the Surface won't boot even the MS-signed "Shim" because the hardware deliberately lacks the "third-party" UEFI certificates... although mjg59 said elsewhere in the thread that allegedly those are now possible to install thanks to the 2023 cert rollover, which actually sounds like it would work (as soon as there's a version of Shim out there that's signed using the 2023 "third-party" cert, and not the 2011 one)