How do I open .ROM and .DSK games using MSX DOS 1?
Are you trying out before getting a real machine?? If so, that’s great to hear! With openMSX you’ll be able to try out an MSX with an MFR or Carnivore2 (with a disk image as SD or CF card) and see how great life is for MSX’ers these days 
if you need help setting that up let me know and I am happy to help!
Actually you'll probably won't ever be able to load a .DSK in such a basic configuration, since disk images are too large to fit on a disk. This is because the disk image is a raw mirror of the entire data on a disk, while on a real disk you always lose some of its nominal capacity to the boot sectors, the file allocation tables and directory data. After copying MSX-DOS files and necessary programs you get even less free space.
So it would make more sense if you're dealing with a fixed disk (like a hard drive or a memory card) on a real system. On an emulated system there's no advantage to load a disk image from MSX-DOS instead of directly mapping it to a drive. The same reasoning could be applied to ROM files, except that they're smaller, and if we're not talking about ROMs larger than 32kB it actually makes some sense. But yet, it would be better just to map the ROM file to a slot.
But anyway, I don't want to rain on your parade. If you want to keep doing random tests, more power to you. I'd also like to help however I can. 
