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.
Best Answer
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.
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