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I have an Acer Iconia W4-820 Tablet which has an Intel Atom Z3740 64-bit CPU, but the Windows version installed on it is 32-bit.

I'm trying to install 64 bit Windows on it by making a bootable USB from a 64 bit Windows ISO image through tools such as Rufus and Windows USB download tool.

But it seems the 64-bit USB isn't able to boot. Only 32-bit boots.

I tried to copy the 64-bit setup files on a 32-bit Recovery Disk created from within the 32-bit Windows, but it showed an error that this application isn't supported because my CPU is 32 bit, which is not true as stated above.

My question is how is the 32 bit Window that's installed causing issues with boot media that's 64 bit to not let it boot from it? AFAIK what happens during the boot should be out of reach of the version of Windows that is installed.

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Your issue is not the CPU; it is the UEFI firmware. UEFI boot in Windows requires the firmware address size to match the OS kernel. The vast majority of systems come with a 64-bit firmware implementation, and most people install 64-bit Windows on top of that. These extremely slim tablets are a recent exception.

The usual alternative is to boot/install Windows in legacy BIOS mode (via UEFI's CSM). However, it's unusual for tablet firmware to implement a CSM, so this is probably not supported.

Note that it's technically possible for an OS to switch to a different mode on boot; however, this is not implemented by Windows 8 or 10 (and comes with some limitations of its own). Linux only implemented it with kernel 3.15, released mid-2014.

While in UEFI mode, the Windows version must match the PC architecture. A 64-bit UEFI PC can only boot 64-bit versions of Windows. A 32-bit PC can only boot 32-bit versions of Windows. In some cases, while in legacy BIOS mode, you may be able to run 32-bit Windows on a 64-bit PC, assuming the manufacturer supports 32-bit legacy BIOS mode on the PC.

Source: Microsoft documentation

See also (inverse problem): How do I install Windows 7 32-bit on a UEFI-based system?, https://social.technet.microsoft.com/Forums/windows/en-US/9b8b18b3-df53-4f00-a584-1b1617b57ea9/windows-7-32bit-uefi-installation?forum=w7itproinstall

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    Its worth pointing out that the Atom Z3740 only supports 4GB of memory. So while technically it does support 64-bit operating systems you likely would see a small performance decrease by doing so unless you have 4GB actually installed because of the small increase use of memory in addresses. Since it came with a 32-bit operating system and as @Bob points out you have a 32-bit UEFI firmware you won't be able to install a 64-bit operating system anyways. It would have to support legacy mode ( which it likely does not ) in order to do that. – Ramhound Mar 1 '15 at 1:39
  • I managed to come up with a solution that should solve the issue . – Damian Nikodem Mar 1 '15 at 16:23
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You are gonna have to hack this a little bit but standard Linux tools are your answer.

Install a boot loader called grub ( use the 32 bit version ) to do your initial bootstrap on the usb and then get that to launch the 64 bit installer and install 64 bit windows to the tablet.

Now uefi will crack it over the OS that is installed on the tablet so you will have to now use a Linux live usb to boot the tablet and install grub on the tablet to circumvent this restriction and point it t boot up your 64 bit windows install.

It's a bit of a moot point to install a 64 bit os on this tablet but I can see a few reasons ( mostly just developing and testing 64 bit code )

  • Can you post the GRUB config or menu entry? – XP1 Nov 1 '17 at 18:32

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