| Company | Nintendo, others |
| Boards | NROM, HROM*, RROM, RTROM, SROM, STROM |
| PRG ROM capacity | 16K or 32K |
| PRG ROM window | n/a |
| PRG RAM capacity | 2K or 4K in Family Basic only |
| PRG RAM window | n/a |
| CHR capacity | 8K |
| CHR window | n/a |
| Nametable mirroring | Fixed H or V, controlled by solder pads (*V only) |
| Bus conflicts | Yes |
| IRQ | No |
| Audio | No |
| iNES mappers | 000 |
The generic designation NROM refers to the Nintendo cartridge boards NES-NROM-128, NES-NROM-256, their HVC counterparts, and clone boards. The iNES format assigns mapper 0 to NROM.
The suffixes 128 and 256 refer to kilobits by Nintendo's own designation; not kilobytes (as is the case with UNROM 512, for example).
All Banks are fixed,
None. This has normally no mapping capability whatsoever! Nevertheless, tile animation can be done by swapping between pattern tables $0000 and $1000, using PPUCTRL bits 4-3 as a "poor man's CNROM".
RROM and SROM are NROM with different CHR ROM pinouts. RTROM and STROM split PRG into two 8KiB ROMs. HROM is an early NROM variant without the solder pads to select mirroring, only vertical mirroring available (as if the 'H' pad were selected).
Family Basic, released by Nintendo, Sharp, and Hudson, contains 2 KiB WRAM (or 4 KiB WRAM for v3) accessible at $6000-$7FFF and decoded with a 74HC20, that is backed with 2 AA batteries. The cartridge is equipped with a back up switch that, when enabled, disables all access to WRAM in order to prevent possible data corruption when the Famicom is turned on or off.
Galaxian uses a smaller 8KiB PRG ROM chip. iNES images are all therefore overdumps.
Modern homebrew programs sometimes use mapper 0 with 8 KB of CHR RAM, which would not be supported on official NROM PCBs without rewiring. In theory, BNROM might be a more appropriate choice. But most emulators will do the right thing with a 16K or 32K PRG ROM with mapper 0.
NROM-368 is a recent invention that allows addressing more memory without bank switching.
Categories: Nintendo licensed mappers, Discrete logic mappers, In NesCartDB