So, I will try to summarize my experience with virtualization software here. I am using virtualization software for running software that isn't runnable on Linux, including Microsoft Office and some programming tools (mostly for LOGO) for Windows, and including old DOS games, my favorite being Prince of Persia. If you have something to comment, please do!
About VirtualBOX:
PROs:
1) Can run Windows 10 without much tweaking (I haven't even managed to run Windows 10 in QEMU). So, it's useful for running Windows Apps under Oracle Linux, since I get a BSOD if I try to install Windows 10 directly on my computer, and WINE also doesn't work well under Oracle Linux (and I get Kernel Panic when I try to install Ubuntu, probably because of the NVIDIA drivers).
2) Useful GUI. I can change which ISO image is mounted once I already started the virtual machine, and there is no obvious way to do that in QEMU.
3) Usable Guest Additions. QEMU Guest Additions simply fail to install under ReactOS with "Entry Point Not Found" error.
4) ReactOS can connect to the Internet with default settings. It can also be done in QEMU, but not with default settings.
CONs:
1) Annoying emulation bugs that cause operating systems to crash. ReactOS appears not to have problems with those, but Windows 10 and FreeDOS do. If you run Windows 10 in VirtualBox, you'll run into BSOD after running DosBox for around half an hour, and after running Kodu for a few minutes, and immediately after running Windows Media Player with visualizations enabled. Disabling hardware acceleration makes it possible to run Windows Media Player with visualizations, but the problems with Kodu and DosBox remain even if all hardware acceleration is disabled. And in FreeDOS, you sometimes get inexplicable Invalid Opcode errors in the kernel (which require you to reset the VM), which don't happen in QEMU. On FreeDOS website, there are instructions about how to prevent that from happening during installation, but it doesn't happen just during installation. Though those bugs appear not affect the most useful programs, such as Microsoft Office or compilers, it can still be annoying.
2) There appears to be no way to get sound to work in FreeDOS, even if you enable SoundBlaster emulation.
About QEMU:
PROs:
1) It claims to be able to emulate many processors that don't belong to the x86 family. From what I've read, it appears that the ARM emulation is good enough to be useful.
2) No Invalid Opcode errors randomly popping up in FreeDOS and requiring you to reset the virtual machine.
3) Emulates AdLib sound card, PC speaker and apparently correctly emulates SoundBlaster, so you can get the sound in DOS games. At lest it's good enough for Prince of Persia 1 to run well.
CONs:
1) QEMU, unlike VirtualBox, has the same default settings for all operating systems. So, it basically requires you to set up everything by yourself. It's annoying, I still haven't found a way to run Windows 10 in it.
2) Guest Additions fail to run on ReactOS.
3) It runs significantly slower than VirtualBox, and it can be seen if you try to run multiple apps in ReactOS at the same time. Enabling hardware acceleration such as KVM helps a little, but not much. So, my guess would be that, even if I manage to run Windows 10 on it, it wouldn't be very useful after all.
CONs of both QEMU and VirtualBox:
1) Attempting to install AC97 sound drivers on ReactOS leads to a BSOD. Attempting to install HDA sound drivers leads to their successful installation... but, when you restart ReactOS, it again claims the sound drivers are not installed. SoundBlaster is not detected by ReactOS at all. I doubt it would be like that on a real machine.
2) Prince of Persia 2 freezes either when the narrator is supposed to comment on the second picture in the introduction, or when the Level 1 starts. Either way, it's not at all playable. I supposed it may be a problem with the default CPU QEMU emulates, however, attempting to make QEMU emulate an ancient CPU leads the FreeDOS Bootloader to fail.
Bonus - about DosBox:
PROs:
1) It doesn't require you to install an actual operating system inside its virtual machine in order to be used.
2) It can run Prince of Persia 2.
3) It can run Windows 3.11 and some games for it. Windows 3.11 fails to install in VirtualBox and QEMU, presumably because of incompatibility of MS-DOS and FreeDOS. Still, in my experience, if a game for Windows 3.11 fails to run directly on 32-bit Windows 10, it also fails to run on Windows 3.11 run in DosBox. Games that try to switch between Windows mode and full-screen MS-DOS mode cause DosBox to freeze, while they simply terminate with an error message if run directly on Windows 10.
CONs:
1) It causes BSOD in Windows 10 if it's run in VirtualBox after around half an hour. So, you can't play DOS games for more than half an hour, or play DOS games while a program is being installed (because you don't know if a BSOD will interrupt the installation).
2) It claims to be runnable under Linux. However, if I try to run it on Oracle Linux, it reports that SDL is not properly installed. And if I try to reinstall SDL, I get a bunch of errors about unresolved dependencies. So, there is no obvious way to run it directly on my computer. And I like stuff that work right out of the box, you know.
3) The operating system in them is not a real DOS, and it doesn't actually behave like one. In some cases, it emulates DOS less accurately than Windows 10 itself (NTVDM) does. This can be especially seen with programming tools. DJGPP fails to install. And, when you are programming for DOS in DosBox, it's very easy to end up relying on DosBox specific behavior without actually knowing that. For instance, a few years ago, I made a decimal to IEEE-754 converter for DOS, and I realized too late that I was relying on DosBox-specific behavior.
About VirtualBOX:
PROs:
1) Can run Windows 10 without much tweaking (I haven't even managed to run Windows 10 in QEMU). So, it's useful for running Windows Apps under Oracle Linux, since I get a BSOD if I try to install Windows 10 directly on my computer, and WINE also doesn't work well under Oracle Linux (and I get Kernel Panic when I try to install Ubuntu, probably because of the NVIDIA drivers).
2) Useful GUI. I can change which ISO image is mounted once I already started the virtual machine, and there is no obvious way to do that in QEMU.
3) Usable Guest Additions. QEMU Guest Additions simply fail to install under ReactOS with "Entry Point Not Found" error.
4) ReactOS can connect to the Internet with default settings. It can also be done in QEMU, but not with default settings.
CONs:
1) Annoying emulation bugs that cause operating systems to crash. ReactOS appears not to have problems with those, but Windows 10 and FreeDOS do. If you run Windows 10 in VirtualBox, you'll run into BSOD after running DosBox for around half an hour, and after running Kodu for a few minutes, and immediately after running Windows Media Player with visualizations enabled. Disabling hardware acceleration makes it possible to run Windows Media Player with visualizations, but the problems with Kodu and DosBox remain even if all hardware acceleration is disabled. And in FreeDOS, you sometimes get inexplicable Invalid Opcode errors in the kernel (which require you to reset the VM), which don't happen in QEMU. On FreeDOS website, there are instructions about how to prevent that from happening during installation, but it doesn't happen just during installation. Though those bugs appear not affect the most useful programs, such as Microsoft Office or compilers, it can still be annoying.
2) There appears to be no way to get sound to work in FreeDOS, even if you enable SoundBlaster emulation.
About QEMU:
PROs:
1) It claims to be able to emulate many processors that don't belong to the x86 family. From what I've read, it appears that the ARM emulation is good enough to be useful.
2) No Invalid Opcode errors randomly popping up in FreeDOS and requiring you to reset the virtual machine.
3) Emulates AdLib sound card, PC speaker and apparently correctly emulates SoundBlaster, so you can get the sound in DOS games. At lest it's good enough for Prince of Persia 1 to run well.
CONs:
1) QEMU, unlike VirtualBox, has the same default settings for all operating systems. So, it basically requires you to set up everything by yourself. It's annoying, I still haven't found a way to run Windows 10 in it.
2) Guest Additions fail to run on ReactOS.
3) It runs significantly slower than VirtualBox, and it can be seen if you try to run multiple apps in ReactOS at the same time. Enabling hardware acceleration such as KVM helps a little, but not much. So, my guess would be that, even if I manage to run Windows 10 on it, it wouldn't be very useful after all.
CONs of both QEMU and VirtualBox:
1) Attempting to install AC97 sound drivers on ReactOS leads to a BSOD. Attempting to install HDA sound drivers leads to their successful installation... but, when you restart ReactOS, it again claims the sound drivers are not installed. SoundBlaster is not detected by ReactOS at all. I doubt it would be like that on a real machine.
2) Prince of Persia 2 freezes either when the narrator is supposed to comment on the second picture in the introduction, or when the Level 1 starts. Either way, it's not at all playable. I supposed it may be a problem with the default CPU QEMU emulates, however, attempting to make QEMU emulate an ancient CPU leads the FreeDOS Bootloader to fail.
Bonus - about DosBox:
PROs:
1) It doesn't require you to install an actual operating system inside its virtual machine in order to be used.
2) It can run Prince of Persia 2.
3) It can run Windows 3.11 and some games for it. Windows 3.11 fails to install in VirtualBox and QEMU, presumably because of incompatibility of MS-DOS and FreeDOS. Still, in my experience, if a game for Windows 3.11 fails to run directly on 32-bit Windows 10, it also fails to run on Windows 3.11 run in DosBox. Games that try to switch between Windows mode and full-screen MS-DOS mode cause DosBox to freeze, while they simply terminate with an error message if run directly on Windows 10.
CONs:
1) It causes BSOD in Windows 10 if it's run in VirtualBox after around half an hour. So, you can't play DOS games for more than half an hour, or play DOS games while a program is being installed (because you don't know if a BSOD will interrupt the installation).
2) It claims to be runnable under Linux. However, if I try to run it on Oracle Linux, it reports that SDL is not properly installed. And if I try to reinstall SDL, I get a bunch of errors about unresolved dependencies. So, there is no obvious way to run it directly on my computer. And I like stuff that work right out of the box, you know.
3) The operating system in them is not a real DOS, and it doesn't actually behave like one. In some cases, it emulates DOS less accurately than Windows 10 itself (NTVDM) does. This can be especially seen with programming tools. DJGPP fails to install. And, when you are programming for DOS in DosBox, it's very easy to end up relying on DosBox specific behavior without actually knowing that. For instance, a few years ago, I made a decimal to IEEE-754 converter for DOS, and I realized too late that I was relying on DosBox-specific behavior.
