guitarzombie wrote:
What does the actual mapper do? Does it just set the limit of what the cart can handle (aside from IRQ stuff which I dont even know what it does)?
The mapper allows access to more memory than the NES can normally handle, by making smaller sections of a larger ROM visible in the small window the NES can see. IRQs are normally used for raster effects, like parallax scrolling or status bars. It may be possible for a game that normally uses IRQs to function without them (it depends on how the game was coded), but these effects will be screwed up.
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They also said they tried it with a SMB 2 lost levels MMC3 hack on MMC1 and it worked but some of the graphics are off.
It's impossible for it to work without modifications. The way the program interfaces with these mappers is completely different. Things like which addresses are used to send commands to the mapper, how the bits should be formatted, everything is different. The only way an MMC3 game would work unmodified on an MMC1 board was if by dumb luck a reasonable amount of executable code ended up mapped to the correct places and the game didn't need to switch banks for a while, but this is highly unlikely.
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MMC1s limits are PRG 256k and CHR 128k and MMC3 are PRG 512k and CHR 256k. If this is possible, it would be nice to be able to use some 128k/128k TLROMs on SLROM.
Comparing mappers is much more complex than looking at how much memory they can address, because the way in which they address it differs a lot from mapper to mapper. Like I said before, the way the program interfaces with the mapper differs, as well as the number and size of the slots in which the address space is divided, the presence and location of a fixed bank... all different. IRQ generators too, are completely different from mapper to mapper, if they're even present (the MMC1 doesn't have it).
guitarzombie wrote:
'the rectangular one is mmc1 and the sqaure one is mmc3 right?'.
Just so you know, there are rectangular MMC3 clones out there.
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He even said he's take a picture and show me.
Trust me, this guy isn't running MMC3 games on MMC1 boards unmodified, that's simply not possible. Games that don't utilize the more advanced features of the MMC3 (finer granularity of PRG and CHR slots, IRQs, etc.) could be hacked to run on an MMC1, but they absolutely must be hacked so that the mapper is correctly interfaced with. If he's claiming anything different he's either deliberately lying or he made a mistake somewhere and misinterpreted the results.