[chungy]

Different use cases than QEMU, honestly, to the point that there's not much overlap. QEMU is extremely good at running modern operating systems, and not so much at older ones (DOS and Win9x are pretty sore points in QEMU). 86Box is extremely good at running old operating systems (including DOS and Win9x!), but modern operating systems are mostly out of the question (you can run WinXP, but https://86box.readthedocs.io/en/latest/usage/faq.html#can-i-...).

[flowerthoughts]

What's missing in qemu for running old OS'?

[adrian_b]

The simulators for running old operating systems must simulate correctly the entire IBM PC, with all its peripherals, not only the CPU.

QEMU simulates some peripherals, e.g. a certain video card, for which it hopes that any operating system that you install includes device drivers. This assumption is no longer true for very old operating systems, which may either lack device drivers or their device drivers may rely on some hardware behavior of the peripherals that is not implemented in QEMU.

Simulators like 86Box simulate an IBM PC clone at a much greater detail, but that is paid by being much slower, so they are not suitable for recent operating systems, which need faster CPUs.