7800 game ROM differences

[+kheller2]

While trying to build a clean group of ROMs for the 7800, I've noticed that some of them are slightly different.. while others are very different. (from a bit comparison)

 

Example:

 

I have two copies of wintergames where only 1 byte is different. The 55nd byte.

 

I have two copies of Waterski, one ROM image is 32896 byes, the other is 131200 bytes. The headers looks a bit different too... while most of them seem to start with "ACTUAL CART DATA STARTS HERE" .. I'm assuming that is leftover from whatever was used to dump the roms and perhaps different dumps from the same program just the program was at a different release level.

 

So, my two questions are:

 

1. Why is there this header?

2. Why such a large file difference?

[cschell]

I'm assuming you're dealing with .a78 files. The header is so the MESS emulator can tell what type of cart it is.

 

I forget how long the header is, but if the 55 byte is in the header, I wouldnt' worry about it. As for the much longer file, someone just made an overdump. (Read in more data than actually existed in the cart.)

 

If you're putting these together for a CC2, you need to use raw BIN files not A78 files though.

 

Chad

[+Mitch]

Just download your 7800 BINs from here and you'll be OK.

 

I believe Chad is correct regarding your files, it sounds like you have the A78 versions. By the way, the header is 128 bytes.

 

The real Water Ski BIN is 64K, the 32K and 128K versions are an underdump and overdump created for the limitation of MESS at the time they were released. As MESS now handles 64K BINs those other versions are no longer necessary.

 

Mitch

[+kheller2]

Mitch,

 

Thanks for the tip on the ROMs. It seems all the ones here at AtariAge are .a78 and many seem to be "overdumps".

 

If I were to strip off the first 128 bytes... anyone know if those ROMs would work on CC2?

 

Answer: tail -c +129 file.a78 > rom.bin is your friend.

[+Mitch]

Mitch,

 

Thanks for the tip on the ROMs.  It seems all the ones here at AtariAge are .a78 and many seem to be "overdumps".

 

If I were to strip off the first 128 bytes... anyone know if those ROMs would work on CC2?

 

Answer:  tail -c +129 file.a78 > rom.bin  is your friend.

 

Yes, if you strip off the header it will work in the CC2.

 

Mitch