qtoyoda wrote:
would someone mind explaining the mappers of an nes rom ?
"Mappers" is how we call the extra hardware present in the carts that is meant to expand the capabilities of the system. You see, there's an entire computer inside a video game console, but there is no software for it to run. The software is in the carts, and you have to plug them in so that the computer has a program to run. The NES was designed with certain limitations to how much memory it can see (32KB of PRG-ROM, 8KB of CHR-ROM/RAM), and the first games that were made actually respected those limitations, so their carts only conteined the memory chips wit the program and the tiles.
But as time went on, games were becoming more complex, and those limitations were getting in the way. Now, you can't change how much memory the NES sees, but you can use a larger memory chip and select which part of it will be visible to the NES at any given time. This means you can have a total of, say, 128KB of PRG-ROM, but the NES will only see 32KB at a time. This works well for games, because you can have different levels, songs, etc. in different banks (as they are called) of memory.
The same concept has been used to overcome the CHR limitation, and since there are a lot of signals present on the cart connector, the carts can monitor/control a lot of other aspects of the machine as well. So Nintendo and other companies started to explore this potential, and and this resulted in the creation of many mappers with different features available to the games.