I'm generally not a huge fan of emulators, preferring to run to run the games on the original systems for which they were made with their original graphics, sound and screen resolutions, but I have been using DOSBox since it came out since it does a good job of running the games as they were, without changing or adding any features. You can use the original saved games... etc.

ScummVM on the other hand, from what I read from their page, does change the executables, which is why I was against using it. I am however about to start my first GOG game that uses it (7th Guest). So could anyone please tell me:

1) Does ScummVM add or change any features in a game? How different is a ScummVM vs native game in general? Does the fact that old saved games aren't compatible mean it uses its own saving system? So you can use ScummVM to creates saves in games that you couldn't originally?

2) Is there any way, when using the GOG version of the game, do get the original files, skip ScummVM and just try your luck with DOSBox. From what I've read the 7th Guest for example runs fine in it, so I have no idea why ScummVM was used...

For some weird reason, this thread doesn't appear in the forum for me, and when I add it to favourites, it appears with -1 replies. Not sure if it appears to others. Hoping this reply will cause number of replies to change to 0 and make it visible.

I also don't like that aspect and I'd like to be able to play the original games in Dosbox too.
(unless they are broken like maybe "I Have No Mouth..")

A: ScummVM usually just kept original flavor. Some new features are added, like enable voice and subtitle at the same time (which are not supported by original version) , or support more languages, show two different subtitles at the same time, etc. A: Usually they are 100% the same with original gameplay. A: ScummVM has its own saving system, so they are not compatible with original ones. And, newer version of ScummVM are not always compatible with its (very) old version saves. A: Yes. A: If GOG installer encluded the original executable, yes you can run it in DOSBox. However, I am not sure if GOG installer included those needed executables.

Not sure what you mean by "changing the executables". As far as I know, ScummVM doesn't change any files. What it is is an engine replacement for a whole lot of old adventure games, meaning that when you run a game through ScummVM, the original game assets are intepreted by the relevant game engine in ScummVM rather than the engine in the game's own executable. As such, the executable is simply bypassed, not changed.

It's like playing Duke Nukem 3D through eDuke32 rather than DOSBox. It's not an emulator, it's an engine replacement.

Also, ScummVM is awesome ;-)

Note about ScummVM. If you check their page there's a compatibility chart. If it's not 100%, then there's bound to be some small changes because the game isn't implemented properly.

The games will generally play exactly like they did on the original hardware, sometimes with an added ScummVM menu you can bring up to save the game which wasn't in the original, but other than that there usually aren't changes made to the game.

However! Especially timing does seem to be a bit off at times. For instance, Day of the Tentacle has slight timing issues meaning an animation will play slightly too long before cutting to the next scene. I played that game way too much as a kid. In the sequence where you're falling through time it seems to take slightly longer than it ought before changing to the next character view, there's about a half second more music before it changes scene, an extra note that wasn't there is kinda noticeable. But hey, this might actually just be because the game didn't run exactly similarly even back in the day. The remastered edition seem to do the same thing.

Omg, I immediately noticed that something was strange..

I played tons of adventures again using ScummVM and never noticed changes compared to the original or when playing them again with DOSBox. I am honestly not sure where you got the idea that ScummVM changes the gameplay.

They have added small features in some games, like mouse support in Sierra's AGI titles, the ability to have subtitles and voices at the same time in games that didn't allow that originally, or an on-screen button to read a particular note again in I Have No Mouth And I Must Scream (I'm not sure about that last one). In a few cases (Monkey Island 1 and 2, for example), they removed the copy protection.
Otherwise, they try to replicate the original game engines as closely as possible. Sometimes, they've even been able to use the original source codes (Beneath a Steel Sky is such a case).

I'm not a big fan of source-ports or changing anything about the games at all, but even I think the people behind ScummVM are doing a terrific job.
In general, I still prefer using DOSbox for games that run in it, but the great thing about ScummVM is that it doesn't just support DOS games, but also titles/versions for Windows, Amiga, C64, etc.

And yes, if a GOG release runs in ScummVM and still has the original EXE in the directory, you can usually drop it into DOSbox and run it that way. The major exception are games where they decided to compress the audio (god knows why), as is apparently the case with Sam & Max Hit the Road and Indiana Jones and the Fate of Atlantis; Dosbox won't be able to properly read those files.

Well on their page they said " The clever part about this: ScummVM just replaces the executables shipped with the games, allowing you to play them on systems for which they were never designed!". I thought it to mean that ScummVM actually changes the executable, as in remove (possible after making a backup of it) the old game.exe and replace with a modified game.exe.

ScummVM usually leave the copy protection as is.
They ONLY remove copy protection when there are official versions that have had removed it. As far as I know, ScummVM has much better MIDI support than DOSbox.
DOSbox do support MIDI, but ScummVM do it better.
ScummVM is a standalone software, supports various games via its internal game engines.
ScummVM never change any files of the original game.

No. The .exe that's being run is simply the ScummVM.exe. It comes with a library of plugins that act as the games engines/interpreters. Nothing is being deleted, the program simply reads the original game files (graphics, sounds, scripts) and interprets them like the game's actual engine would have.

Since it's not an emulator but an engine replacement, there is a chance they didn't recreate the engine perfectly, even if they had the source code of the originals (which they didn't in all cases). And from the posts here it does seem they made some changes to the games (subtitles, saves...). I know these are mostly minor changes and they're improvements, but for each person there is a different line that a minor improvement can cross so that the new game is no longer like the original. I tried it for the 7th Guest, but it seems that it's not as straightforward. It needs the proper CD images mounted, and I really don't feel like playing around with the files GOG has (the largest is 89 MB; none appear to be the images) to see if I can reconstruct them. :( But just to confirm: if I don't bring up the ScummVM menu, then I can still use the game's original save system normally (including not being able to save if the original game didn't allow it), right?

I don't think ScummVM changes your existing game installation (by replacing exes or any other files). Instead, you tell ScummVM where the data files for a supported game is (existing installation, original CD, GOG installation...), and it copies them to the ScummVM. You normally run the game through the ScummVM application. Or at least that's how I remember it the last time I tried it...

I've played through the GOG (ScummVM?) version of 7th Guest, and I don't recall it feeling or looking any different than the original CD version I played many many years ago.

So some retrogamers still hunt down old hardwares to run old games. :-)
DOSbox also can not provide 100% original runtime environment. Only true hardwares do.

Maybe you have to hunt down the original CDs.

Only when you are not running ScummVM.
If you run the game in DOSbox, you can use those original saves.
ScummVM never touch those files, it just read resources files it needed.

Since ScummVM use its own saving system, you can not use those original saves in ScummVM.