[cmrdporcupine]

Really when people say x86 now tho they don't mean that. They really mean the variant introduced with the 386 which has a linear memory model, memory protection, etc. Or x86_64 which is philosophically akin to the 386 but really a new ISA.

So it's really more like mid-80s or early 2000s, not late 70s.

[M95D]

^ that!

You can't run a COM program today. Not without emulation. Recent PCs can't even run DOS EXE because they're missing the BIOS interrupts most DOS programs use.

[mifydev]

You can just boot freedos to run them, it will execute in real mode which has the same cpu instructions as 40 years ago.

[M95D]

UEFI switches the CPU into 32bit v86 mode or directly in 64bit mode and you can't go back to real mode without a CPU reset, which v86 won't allow (you don't have ring -2 privileges) and 64bit mode can't do at all. I don't have a UEFI system, so I might be wrong (I even hope I'm wrong - it would mean slightly more freedom still exists), but from what I read about it, I'm 90% certain it's not possible.

[rep_lodsb]

You're confusing several things here. The only x86 processor that didn't allow returning to real mode was the 16-bit 80286 - on all later ones it's as simple as clearing bit 0 of CR0 (and also disabling paging if that was enabled).

Nothing more privileged than ring 0 is required for that.

"v86" is what allowed real mode to be virtualized under a 32-bit OS. This is no longer available in 64-bit mode, but the CPU still includes it (as well as newer virtualization features which could be used to do the same thing).

[M95D]

You can write to CR0 from a DOS COM program while in V86 mode??? :o Wouldn't that cause a GPF / segfault / EMM386 crash?

[yjftsjthsd-h]

Can you boot freedos on new hardware? I was under the impression that it needs BIOS/CSM and that may or may not be an option on new machines.

[cmrdporcupine]

Even if you could/can it is an anachronism. Architecturally there's just a huge difference between 8086 and even 80286 and the 386. Before the 386 I wouldn't touch a machine with an Intel processor in it. Once the 386/486 penetrated the market and became cheap it was game over for everything else because it was good enough (linear address space, memory protection, larger address space, 32-bit etc etc), smart enough, gosh darn it it was cheap and everywhere.

[anthk]

No, you are wrong. DOS COM files if 16 bit can't be run on 64 bit CPU's but 32 bit DOS binaries can be run under 32 bit GNU/Linux installs with DosEMU straight by just emulating the BIOS part, the rest is native.

[rep_lodsb]

It has nothing to do with being unable to run 16-bit code, that's a myth.

https://man7.org/linux/man-pages/man2/modify_ldt.2.html

Set seg_32bit=0 and you can create 16-bit code and data segments. Still works on 64 bit. What's missing is V86 mode, which emulates the real mode segmentation model.

[anthk]

That can be trapped for sure.

[M95D]

You actually confirmed what I said. :)

[anthk]

50/50, because once you boot a 32 bit os you can run 16 bit binaries :)

I'm pretty sure that if I make a dual-kernel 9front (9pc and 9pc64 available at boot) in a 64 bit machine and I compile emu2 for it, DOS COM binaries might be trapped enough to run simple text mode tools under the 386 port.