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Benjamin Auquite edited this page Nov 22, 2025 · 2 revisions

KotOR RIM File Format Documentation

This document provides a detailed description of the RIM (Resource Information Module) file format used in Knights of the Old Republic (KotOR) games. RIM files store template resources used as module blueprints.

Table of Contents

File Structure Overview

RIM files are similar to ERF files but are read-only from the game's perspective. The game loads RIM files as templates for modules and exports them to ERF format for runtime mutation.

RIM vs. ERF/MOD

While RIM files share structural similarities with ERF/MOD files, they serve different purposes:

RIM Files:

  • Stored as <module_name>.rim and <module_name>_s.rim (secondary/localized)
  • Read-only template data - never modified during gameplay
  • Contain base module resources before player modifications
  • Typically paired with corresponding ERF files during development

Module Loading Process:

  1. Game loads the RIM file as the base template
  2. If a save exists, corresponding SAV file overrides modified resources
  3. Override folder and HAK files can replace specific resources
  4. Runtime changes (opened doors, looted containers) are saved to SAV, not RIM

Extended RIM Files:

Files with '_s' suffix (e.g., module001_s.rim) are "extended" RIM files:

  • Contain additional or updated content for the base module
  • Loaded after the primary RIM but before player saves
  • Often used for patches or expansion content
  • Include an extended header (104 additional bytes)

Implementation: Libraries/PyKotor/src/pykotor/resource/formats/rim/

Reference: vendor/reone/src/libs/resource/format/rimreader.cpp:24-100

Binary Format

File Header

The file header is 20 bytes (or 124 bytes with extended header):

Name Type Offset Size Description
File Type char[4] 0 4 Always "RIM " (space-padded)
File Version char[4] 4 4 Always "V1.0"
Unknown uint32 8 4 Typically 0x00000000
Resource Count uint32 12 4 Number of resources in the archive
Offset to Resource Table uint32 16 4 Offset to resource entries array

Reference: vendor/Kotor.NET/Kotor.NET/Formats/KotorRIM/RIMBinaryStructure.cs:13-53

Resource Table

Each resource entry is 32 bytes:

Name Type Offset Size Description
ResRef char[16] 0 16 Resource filename (null-padded, max 16 chars)
Resource Type ID uint32 16 4 Resource type identifier
Resource ID uint32 20 4 Resource index (usually sequential)
Offset to Data uint32 24 4 Offset to resource data in file
Resource Size uint32 28 4 Size of resource data in bytes

Reference: vendor/reone/src/libs/resource/format/rimreader.cpp:40-70

Resource Data

Resource data is stored at the offsets specified in the resource table:

Name Type Description
Resource Data byte[] Raw binary data for each resource

Extended Header

Extended RIM files (filenames ending in 'x', e.g., module001x.rim) have an additional 104 bytes after the standard header:

Name Type Offset Size Description
IsExtension uint8 20 1 Flag indicating extended RIM (1 = extension)
Reserved byte[99] 21 99 Reserved bytes
Compression uint32 120 4 Compression type (typically 0 = none)

Extended Header Purpose:

The extended header was added to support additional module features:

  • Modular Updates: Extended RIMs can patch or add to base modules without replacing them entirely
  • Compression Support: Reserved space for future compression (though KotOR doesn't use it)
  • Versioning: Allows identification of expansion/patch content

Usage Example:

module001.rim   - Base module (Endar Spire)
module001_s.rim  - Extended content (additional areas or restored content)
module001_dlg.erf  - Dialog for the module (weird quirk exclusive to K2/TSL)

The game loads both files, with the extended RIM's resources taking precedence over conflicting base RIM resources.

Identifying Extended RIMs:

Extended RIMs can be identified by:

  1. Filename ending in 'x' (e.g., danm14aax.rim)
  2. IsExtension flag = 1 in the extended header
  3. Total header size of 124 bytes instead of 20 bytes

Standard RIMs that aren't extended can still function normally even if parsers check for the extended header - they'll simply find the resource table immediately after the 20-byte header.

Reference: vendor/Kotor.NET/Kotor.NET/Formats/KotorRIM/RIMBinaryStructure.cs:40-50

Implementation Details

Binary Reading: Libraries/PyKotor/src/pykotor/resource/formats/rim/io_rim.py

Binary Writing: Libraries/PyKotor/src/pykotor/resource/formats/rim/io_rim.py

RIM Class: Libraries/PyKotor/src/pykotor/resource/formats/rim/rim_data.py:87-158

This documentation aims to provide a comprehensive overview of the KotOR RIM file format, focusing on the detailed file structure and data formats used within the games.

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