Originally posted by: dra600n
Pier Solar is 64 megabit (it's an 8MB rom), Paprism is 80 megabit (10MB) which is the largest the Genesis can handle due to address spaces of the 32x and Sega CD. You could go past these boundaries I believe, but it won't work with the devices connected (amongst other issues I'm sure).
The maximum for Genesis cartridges is 32Mbit (4MB). 80Mbit requires using up the Sega CD and 32X address spaces. Sega forbid licensed developers from using more than the 32Mbit maximum. Pier Solar (also Super Street Fighter II) use a mapper in the cartridge to get past the 32Mbit limit while still retaining Sega CD and 32X compatibility. Paprium will likely use a mapper chip too. Apparently it's using a co-processor which can decompress data and mix audio.