Reply 20 of 53, by mr_bigmouth_502
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wrote:That's partly just it... DOSBox only "emulates" the bare minimum to get games to work. […]
That's partly just it... DOSBox only "emulates" the bare minimum to get games to work.
There is no BIOS, it simulates a BIOS for BIOS calls, but the actual data area of the BIOS is practically empty. This can be seen quite clearly in Ultima 7. There is a screen during the intro that is supposed to be video snow effect (like tuning to an empty channel on an old TV set.) The game does it by using the BIOS area (read only,) to generate a semi-random (but steady) binary sequence. In DOSBox (without a handy patch someone wrote,) you get a Black screen with a few white specs throughout.
When we get to the other features, including the video features, it simulates the presence of the HW. Which is why you don't have to hunt down and download the ROM files for the cards like you do with true emulators (such as PCem.) They know how the card responds to different calls, and just use those responses. If you trace backwards the functionality with previous DOSBox versions, you can see how this has been tweaked, fixed, improved, etc... over time.
In the end, there is quite a bit of functionality that is never realized (or is lost,) compared to a real PC. Such things as true system speeds (it's only approximated,) some strange/fancy install procedures, and other such. About the only thing they worry about is, "will the game play?" If a game doesn't play, they look into why. If a game doesn't install correctly, they don't worry as much about it. On several occasions, I've had to install the game on a real PC, then pack up the directory and move it to my DOSBox "C" drive.
They themselves have referred to it as a "DOS" emulator for games. If it is an emulator, it emulates an OS, and not a machine. To me, that is a defining difference between emulation and simulation. It simulates an older machine through OS emulation. It makes it easier to use, in a way, but reduces complete compatibility.
With all that in mind, how can we assure that DosBox actually runs games the same way they would run on an actual PC? How do we know that it's not just running them in a manner that is only superficially similar, like ZSNES does for SNES emulation?