I have installed MS-DOS 6.22 (released in 1994) on Virtual Box, and I want to know if Virtual Box is emulating an ISA bus or a PCI bus. The settings for my virtual machine don't show any information about the bus.
If you went with VirtualBox's default settings for an MS-DOS system, you've got both: an Intel 440FX northbridge providing a PCI bus, and an Intel PIIX3 southbridge connected to that bus, providing an ISA bus. The virtual video card (generic VESA-compatible) and PCnet-FAST III network card will be attached to the PCI bus. The sound card (a virtualized SoundBlaster 16) will be attached to the ISA bus. The hard drive and CD-ROM will be on a PIIX4 connected to the PCI bus.
(Source: attaching a SysRescueCD to an MS-DOS VM and seeing what the diagnostics had to say.)