nes-formatlisted

# NES ROM Format Reference Three ROM formats exist: **iNES**, **NES 2.0**, and **UNIF**. NES 2.0 is the current standard and recommended for new dumps. UNIF is deprecated. ## Format Detection Quick Guide | Signature in file | Format | |-------------------|--------| | `NES` + `$1A` + byte 7 bits 3-2 = `10` | NES 2.0 | | `NES` + `$1A` + byte 7 bits 3-2 ≠ `10` | iNES | | `UNIF` | UNIF | --- ## iNES Format (.nes) Created by Marat Fayzullin for the iNES emulator. Uses an 8-bit mapper number (0–255). Bytes 8–15 are loosely defined and vary between iNES revisions. NES 2.0 repurposes them with a formal specification. ### File Layout ``` [16-byte Header] [optional 512-byte Trainer] [PRG-ROM data] [CHR-ROM data] ``` Some ROM images also have a 128-byte title at the end of the file. ### Header Byte Map | Byte | Field | |------|-------| | 0–3 | `$4E $45 $53 $1A` — "NES" + MS-DOS EOF | | 4 | PRG-ROM size in 16KB units | | 5 | CHR-ROM size in 8KB units (0 = CHR-RAM used) | | 6 | Flags 6: `NNNN FTBM` | | 7 | Flags 7: `NNNN xxTT` | | 8 | PRG-RAM size in 8KB units (0 infers 8KB for compatibility) | | 9 | TV system: bit 0 = 1 if PAL | | 10 | Unofficial extension: TV system, PRG-RAM presence, bus conflicts | | 11–15 | Padding (should be zero, but some tools wrote identifying strings here) | ### Byte 6 Flags (`NNNN FTBM`) | Bit | Name | Meaning | |-----|------|---------| | 0 | M | Nametable arrangement: 0 = vertical mirroring, 1 = horizontal mirroring | | 1 | B | Battery-backed PRG-R