DOSBox executes all DOS programs in real mode unless they explicitly enable V86 mode/protected mode. It's an emulator, it doesn't try to execute the privileged instructions on the host system. How do you think it runs on non-x86 systems like arm or powerpc if it's using V86 mode? Excuse me, but do …

jmarsh wrote on 2020-07-22, 04:00: All DOS programs start in real mode. If DOSBox didn't support real mode it wouldn't be able to run anything. It's not real "real mode", but v86 mode. Privileged instructions / Sensitive instructions can run under real "real mode". DOSBox doesn't support them.

cup386.com is not for DOSBox. DON'T use it under DOSBox. Use it under pure DOS. cup386 itself should runs under real mode, then it will enter 386 protected mode and starts unpacking. DOSBox can not offer real mode. That's why it freezes.