INES Mapper 151

iNES Mapper 151 represents the VRC1 on the Vs. System. Given that iNES has a bit to mark "For Vs. System", this assignment was erroneous and any games marked thus should be iNES Mapper 075 instead.

Some emulators treat this as "mapper 75 with hardwired mirroring", rather than letting the "four screen" or "Vs. System" flags override mapper 75's normal ASIC-controlled mirroring. Since Vs. System by definition has 4K of NTRAM, and no other games are known that rely on this definition of hardwired mirroring, separating these mappers seems artificial.

It is remotely conceivable that this is not true: FCEUX-2.1.5's and Nestopia-1.4.0's implementations of mapper 151 do not attach the 5th bit of CHR bank onto the lower 4 and instead emulate all registers as 8 bits wide.

However, no Vs. System games have more than 64KiB of CHR to verify the correct behavior against, and it is unlikely that a separate ASIC was made just for Vs. System games.

Pictures of the Vs. System Gradius module (here, scroll down to "Vs. Gradius") show the same VRC1 as in NesCartDB