How can I find differences between NES ROM?

[Code Monkey | 2,011]

I think it's time I finally document differences from retail across all of my prototypes however I have no idea how to do that outside of playing them each one by one. I have a Gaunlet prototype with a different music track on level 1 so that's an easy one to find but I also have a Mega Man 3 prototype where one specific enemy in one specific stage is slightly shifted to one side by about a pixel. Even if there were differences in the binary code, how would anyone map that to a single enemy being shifted by a single pixel?

[the_wizard_666 | 1,325]

Paging @0xDEAFC0DE

It's easy to compare the binaries to know there are differences, but I wouldn't mind knowing how to determine what they are as well.  Though my assumption would be that it varies depending on the game.

[SNESNESCUBE64 | 541]

If you are talking about comparing binaries, software like Beyond Compare 4 can do that. I use it at work and quite like it. HxD can also do comparisons but it isn't as good.

[fcgamer | 4,727]

10 hours ago, Code Monkey said:

I think it's time I finally document differences from retail across all of my prototypes however I have no idea how to do that outside of playing them each one by one. I have a Gaunlet prototype with a different music track on level 1 so that's an easy one to find but I also have a Mega Man 3 prototype where one specific enemy in one specific stage is slightly shifted to one side by about a pixel. Even if there were differences in the binary code, how would anyone map that to a single enemy being shifted by a single pixel?

You should focus your YT channel around this. I'm sure it would be a huge hit...

[the_wizard_666 | 1,325]

4 minutes ago, SNESNESCUBE64 said:

If you are talking about comparing binaries, software like Beyond Compare 4 can do that. I use it at work and quite like it. HxD can also do comparisons but it isn't as good.

I think he wants to know how to determine what the differences actually equate to within the ROM.  He has a bunch of protos that are very similar to the released games but are a few bytes off when comparing binaries.  He wants to document what those differences equate to in game.

[final fight cd | 187]

12 hours ago, Code Monkey said:

II also have a Mega Man 3 prototype where one specific enemy in one specific stage is slightly shifted to one side by about a pixel. Even if there were differences in the binary code, how would anyone map that to a single enemy being shifted by a single pixel?

How were you able to find this extremely small change?

[Code Monkey | 2,011]

4 hours ago, fcgamer said:

You should focus your YT channel around this. I'm sure it would be a huge hit...

Thanks, that's the plan for the next few videos if I can figure this out.

 

2 hours ago, final fight cd said:

How were you able to find this extremely small change?

I only know from Hidden Palace and The Cutting Room Floor, two websites focused on finding things in ROM. My Mega Man 3 prototype is well known and documented but my Mega Man 2 is unreleased and has never been documented by anyone before. While the ROM has been dumped, it has not been released and I would like to keep it that way which means I need to do it myself.

[Sumez | 2,964]

Finding the difference between two binaries is pretty easy. Figuring out what that difference means is nearly impossible without reverse engineering the part that uses it. 

Easiest start would be firing up Mesen's debugger with a breakpoint on reads or executes from the affected address ranges. But you'd still have to play the game to the point where the difference appears. 

[Tanooki | 4,934]

12 hours ago, fcgamer said:

You should focus your YT channel around this. I'm sure it would be a huge hit...

@Code Monkey I'd watch that.  I bother with a short list of YT stuff as far as subbing goes, they have to do something unique and entertaining, not just someone who spins the same stuff re-using other easily found stuff while coin begging.  Sharpolis does a dive, MVG(not subbed) does as well, Jeremy Parish, gaming historian, GTV Japan, RndStranger (Famidaily), and a few others are worth the look.  If someone focused around nothing but vintage game protos, differences from retail, just ones that didn't retail, and they didn't do it in some cry for attention and money format but presented things tightly like those types I listed do I'd keep up.