dat Files and Formats

dat Files and Formats

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flowchart LR
  subgraph world["World data"]
    map["map.dat"]
    attrib["attrib.dat"]
    event["event.dat"]
  end
  subgraph entities["Entities & rules"]
    monsters["monsters.dat"]
    items["items.dat"]
    spells["spells.dat"]
    roster["roster.dat"]
  end
  attrib -- selects tileset --> map
  map -- bit 0x80 --> event
  event -- OP_12 --> monsters
  items -- use byte --> spells
  roster -- equips --> items
  roster -- knows --> spells

Loading

MM2-local inventory and current format status for data files in this workspace.

[TOC]

MM2-Local Inventory

Canonical set in project root (same bytes are mirrored under EXTRACTED/ and MM2BOOT/):

• attrib.dat - 3840 bytes
• event.dat - 95687 bytes
• items.dat - 5120 bytes
• map.dat - 30720 bytes
• monsters.dat - 6656 bytes
• roster.dat - 8320 bytes
• spells.dat - 256 bytes
• str.dat - 7808 bytes

GOG/PC .DAT compression (confirmed against a real GOG install)

The GOG DOS build wraps some .DAT files in the same custom LZW codec used by the PC .4/.16 graphics (lzw_decompress traced to MM2.EXE @0x2A42; see 54-pc-dos-graphics-formats.md). Detection/decompression: Python tools/pc_dat_lzw.py (canonical LZW impl shared via tools/mm2_lzw.py); C++ editor/src/core/PcDatLzw.{h,cpp}, wired into AttribFile/MonstersFile/StrFile/MapFile/EventFile's load().

GOG file	Container	Result vs Amiga file
ATTRIB.DAT	flat (u32 LE size + LZW, whole file)	byte-identical to attrib.dat
MONSTERS.DAT	flat	byte-identical to monsters.dat
STR.DAT	flat	decodes cleanly to 7707 bytes (Amiga is 7808 — different platform string table, not a decode error)
MAP.DAT	table: u16 LE[60] offset table (one 512-byte screen blob per entry, each u32 LE size + LZW)	reassembled 60 screens byte-identical to map.dat
EVENTSI.DAT + EVENTSO.DAT	table: u32 LE[71] offset table each (indoor / outdoor halves of the 71 event.dat locations; mutually exclusive per slot)	merged (71x6-byte BE header + concatenated blobs) reproduces event.dat to within 18/95687 bytes — all single-byte platform content differences (same offsets/lengths; verified 0x02 Amiga vs 0x01 PC at each diff), not decode errors
ITEMS.DAT	plain (not compressed)	byte-identical to items.dat
ROSTER.DAT / SPELLS.DAT / DEFAULT.DAT	plain (not compressed)	different size from the Amiga file (e.g. SPELLS.DAT 192 bytes vs spells.dat 256) — a structural/record-layout difference between platforms, out of scope here

Both table containers reuse the MONSTERS.4/.16 combat-atlas convention: entry[0] == table_byte_size (also slot 0's blob offset) for MAP.DAT (which never has an empty first screen); EVENTSI.DAT/EVENTSO.DAT instead use a fixed 71-slot count since slot 0 can legitimately be empty in either half. entry[k] == 0 always means "no blob for slot k".

The editor's EventFile::load() tries plain event.dat first, then falls back to EVENTSI.DAT+EVENTSO.DAT auto-merge if only those exist. Saving from the editor always writes plain Amiga-format .dat files (round-trip back to the GOG-compressed shape is not wired into the editor's save path); tools/pc_dat_lzw.py --compress re-compresses the flat container for offline round-trip testing, reusing the verified LZW compressor from tools/encode_pc_gfx.py.

Confirmed Formats

items.dat (confirmed)

Cross-validated with:

• MM2 asset filename references in binary (items.dat appears with spells.dat near code offset 0x29868)
• Legacy reverse code: C:\_20260421_\D-REC\development\Amiga\Smite-and-Magic\Blitz3d\b3dmm2\Item_ED.bb

Layout:

• 256 records
• 20 bytes per record (0x14)
• Record fields:
  • 0x00..0x0B - item name (12-byte ASCII, space-padded)
  • 0x0C - separator/pad (editor writes 0)
  • 0x0D - usable-by bitmask
  • 0x0E - bonus packed nibble (hi=bonus_type, lo=bonus_amount)
  • 0x0F - effect packed nibble (hi=effect_type, lo=effect_amount)
  • 0x10 - damage byte
  • 0x11 - pad/unused byte (editor writes 0)
  • 0x12..0x13 - gold (uint16 little-endian on disk; shop price in gp; game byte-swaps each record word on load, asm 0x26030)

Notes:

• 5120 = 256 * 20, which matches the editor loader/saver loops.
• Item names align 1:1 with b3dmm2/items.txt.

roster.dat (confirmed layout + C loader/saver)

Cross-validated with:

• MM2 executable ASM (EXTRACTED/mm2.asm, EXTRACTED/mm2.capstone.asm)
• New C codec in EXTRACTED/decomp/mm2_roster_codec.h + .c

Layout:

• 64 records
• 130 bytes per record (0x82)
• Key fields:
  • 0x00..0x0A - character name (11-byte ASCII)
  • 0x0B - town/inn byte (low7=town, bit7=party flag inferred)
  • 0x0C - sex
  • 0x0D - alignment (current)
  • 0x0E - race
  • 0x0F - class
  • 0x10..0x15 - current core stats
  • 0x27 - current endurance
  • 0x28..0x39 - equipped items (6 slots x 3 bytes)
  • 0x3A..0x4B - backpack items (6 slots x 3 bytes)
  • 0x4C..0x57 - spellbook bytes
  • 0x58..0x61 - SP/HP/Gems words (little-endian)
  • 0x62..0x65 - XP (little-endian dword)
  • 0x66..0x69 - Gold (little-endian dword)
  • 0x6A..0x73 - base alignment/stats/level/spell-level/endurance
  • 0x74..0x75 - HP current (word)
  • 0x76..0x81 - unresolved tail bytes

Notes:

• Loader/saver round-trips unknown spans byte-for-byte.
• The codec treats numeric multibyte fields in roster.dat as little-endian on disk.

monsters.dat (confirmed record geometry + C loader/saver)

Cross-validated with:

• MM2 executable ASM loader path (allocates/reads 0x1A00 bytes for monsters.dat)
• MM2 accessor routine around 0x99C8 (mulu #$1a, then copies exactly 26 bytes)
• C codec in EXTRACTED/decomp/mm2_monsters_codec.h + .c

Layout:

• 256 records
• 26 bytes per record (0x1A)
• Record shape currently modeled as:
  • 0x00..0x0D - monster name (14-byte fixed field)
  • 0x0E..0x19 - 12-byte stat/behavior payload (still being field-lifted)

Notes:

• This is sufficient for byte-perfect load/edit/save and safe round-tripping.
• Field-level semantics for the 12-byte payload remain TODO pending deeper combat call-site traces.

str.dat (confirmed encoding, partial semantics)

Encoding:

• Byte transform: decoded char = (encoded + 0x1C) & 0xFF
• 0x01 acts as newline/line break

Observed content:

• Contains many in-game text strings (jokes, prompts, shop/guild text, menu/help text).

map.dat (confirmed)

Cross-validated with:

• MM2 executable ASM (flat load into A4-$EEF4, 3D hood reads page 0 @ 0x2900)
• editor/src/core/MapFile.{h,cpp} — 60 screens × 512 bytes
• Collision 0x80 event alignment vs event.dat triplets

Layout:

• 60 map screens
• 512 bytes per screen (0x200)
• Per screen:
  • 0x000..0x0FF — page 0 (visual): 16×16 grid; four 2-bit wall fields per cell (N/E/S/W)
  • 0x100..0x1FF — page 1 (collision): same geometry; (dark<<1)|wall per direction; bit 0x80 = event flag

Notes:

• 30720 = 60 × 512, which matches the editor loader/saver loops.
• Row 0 on disk = south; MM2ED and wiki grids draw north-up.
• Full field decode: map.dat format.

Decoded formats

• event.dat (95687 bytes) — 71 location records; see 06-event-dat-format.md, 07-event-script-opcodes.md, 08-event-runtime.md
• spells.dat (256 bytes) — see 19-spells-and-item-use.md
• attrib.dat (3840 bytes) — see 12-attrib-dat-format.md

Partially Characterized / TODO

These files still need additional field-level work against ASM call sites:

• (none of the primary .dat containers remain fully TODO)

Working rule:

• Use ASM first (EXTRACTED/mm2.capstone.asm, EXTRACTED/mm2.asm) to identify true runtime reads/writes.
• Use legacy Blitz3d reverse code as a cross-check.
• Resolve conflicts in favor of observed assembly behavior.

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See also

Page	Why
items dat Format	256 items
map dat Format	Visual + collision pages
Events by Location	71 per-map script pages
event dat Format	event.dat container
MM2ED Editor	Edit in GUI