[dwattttt]

Intel backwards compatibility has meant that real mode is still with us more of less, but to give context to people who aren't as familiar: real mode was superseded by protected mode with the introduction of the 80286, in 1982.

[BobbyTables2]

I believe Microsoft removed support for 16bit Windows applications some time ago.

The hardware may be willing but the software is now incapable.

[dwattttt]

Yes, as sibling noted, 64bit Windows dropped support for running 16bit applications (which require real mode).

I don't recall seeing a technical justification, however I suspect it's related to what CPU state transitions are allowed; protected mode (32bit) is allowed to swap to "virtual-8086" mode, which I guess is how real mode applications were run (rather than the processor completely turning off virtual memory, or completely emulating a CPU a la qemu).

IA32e mode (Intel's name for X64) however is not allowed to transition into virtual-8086 mode[0]; it has to drop the processor into 32 bit mode first. That would chop off the top level of page tables, so short of something you do to affect the whole machine, that sounds like a non-starter for running an application.

[0] Intel software developer manual 3, 2.2

[bigstrat2003]

Yes, that was removed with the 64-bit versions of Windows. My understanding is because they were using a compatibility layer to run 16-bit apps, and with 64-bit Windows they changed that compatibility layer to run 32-bit apps. But I'm not a Windows internals expert so I could be mistaken.