Format comparison

Overview

Cabriolet supports seven distinct Microsoft compression formats, each designed for specific use cases and historical contexts. This page provides a comprehensive comparison to help you understand the differences and choose the right format for your needs.

Quick Comparison Table

Feature	CAB	CHM	HLP	KWAJ	LIT	OAB	SZDD
Primary Use	Software distribution	Help files	Windows 3.x help	File compression	E-books	Outlook data	Single file compression
Multi-file Support	Yes	Yes	Yes	No	Yes	Yes	No
Compression Algorithms	None, MSZIP, Quantum, LZX	LZX	LZ77	LZSS, MSZIP, Quantum	DES + LZ	LZ	LZSS
Max Uncompressed Size	2GB per folder	Unlimited	16MB	2GB	Unlimited	2GB	2GB
Metadata Support	Extensive	Rich	Basic	Minimal	Rich	Minimal	Minimal
File Attributes	Full Windows	Limited	None	Basic	None	Basic	Basic
Timestamps	MS-DOS format	None	None	MS-DOS format	None	None	MS-DOS format
Multi-part Archives	Yes (spanning)	No	No	No	No	No	No
Embedded Archives	Yes	Yes	No	No	No	No	No
Compression Ratio	Good-Excellent	Excellent	Good	Good	Good	Moderate	Good
Extraction Speed	Fast-Moderate	Fast	Fast	Fast	Slow	Fast	Very Fast
Era Introduced	Mid-1990s	Late 1990s	Early 1990s	Mid-1990s	Early 2000s	Late 1990s	Early 1990s

Detailed Format Analysis

CAB (Cabinet Files)

Purpose and History

Cabinet files were introduced by Microsoft in 1996 as part of Windows 95. They became the standard format for software distribution, Windows updates, and installer packages.

Technical Characteristics

• File Extension: .cab

• Magic Bytes: MSCF (0x4D534346)

• Structure: Multi-folder, multi-file with sophisticated metadata

• Compression Types:

  • None (Type 0) - Store only

  • MSZIP (Type 1) - Deflate-based, block compression

  • Quantum (Type 2) - Proprietary quantum algorithm

  • LZX (Type 3) - Advanced sliding window compression

When to Use CAB

• Software installers and update packages

• Large software distributions requiring multiple CDs

• Windows component updates

• Application deployment requiring file integrity

• Archives requiring strong compression with good speed

Advantages

• Industry-standard format with broad tool support

• Excellent compression ratios with LZX

• Multi-volume support for large distributions

• Rich metadata and file attributes

• Digital signature support

Limitations

• 2GB limit per folder (not per archive)

• Complex structure can slow down small archives

• Quantum compression is proprietary and less efficient

CHM (Compiled HTML Help)

Purpose and History

CHM files replaced the older HLP format in Windows 98. They were designed to provide rich, HTML-based help documentation with full-text search and navigation.

Technical Characteristics

• File Extension: .chm

• Magic Bytes: ITSF (Internal Title Storage Format)

• Structure: Compound file with multiple streams

• Compression: LZX compression exclusively

• Features: Index, full-text search, navigation hierarchy

When to Use CHM

• Software documentation and help systems

• Technical manuals requiring HTML rendering

• Knowledge bases with cross-referencing

• Documentation requiring search capabilities

Advantages

• Rich HTML content with CSS and JavaScript

• Built-in full-text search engine

• Tree-based navigation structure

• Excellent compression for HTML/text content

• Native Windows support

Limitations

• Windows-only format (limited cross-platform support)

• Security restrictions in modern Windows versions

• Cannot be easily edited without specialized tools

• Not suitable for non-HTML content

HLP (Windows Help)

Purpose and History

The original Windows Help format, introduced with Windows 3.0. Widely used throughout the 1990s but deprecated in favor of CHM.

Technical Characteristics

• File Extension: .hlp

• Magic Bytes: ?_ (0x3F5F) or LN (0x4C4E)

• Structure: Binary format with topic-based organization

• Compression: LZ77 variant (Phrase compression)

• Maximum Size: 16MB uncompressed

When to Use HLP

• Legacy software documentation

• Converting old help files to modern formats

• Archival of historical documentation

• Windows 3.x/95 compatibility requirements

Advantages

• Simple, straightforward format

• Fast decompression

• Small file sizes for the era

• Good compression for text content

Limitations

• 16MB size limit

• Deprecated format (no native support in Windows 10+)

• Limited multimedia support

• Outdated text formatting capabilities

KWAJ (Compressed Files)

Purpose and History

KWAJ is a general-purpose compression format used internally by Microsoft for various utilities and installation packages.

Technical Characteristics

• File Extension: Various (often .ex_, .dl_)

• Magic Bytes: KWAJ (0x4B57414A) or SZDD (variant)

• Structure: Single compressed file

• Compression: LZSS, MSZIP, or Quantum

• Header: Contains original filename and metadata

When to Use KWAJ

• Single file compression with metadata

• Distribution of renamed compressed files

• Compression with original filename preservation

• Legacy file decompression

Advantages

• Preserves original filename

• Multiple compression algorithm support

• Simple single-file format

• Good compression ratios

Limitations

• Single file only (no multi-file archives)

• Less common than CAB format

• Limited tool support

• Proprietary format

LIT (Microsoft Reader E-books)

Purpose and History

LIT files were Microsoft’s e-book format for the Microsoft Reader application, used from 2000 to 2011. The format combined DRM with compression.

Technical Characteristics

• File Extension: .lit

• Magic Bytes: ITOLITLS (encapsulated OEB)

• Structure: Compound document with encryption

• Compression: DES encryption + LZ compression

• Content: HTML-based text with images

When to Use LIT

• Reading archived Microsoft Reader e-books

• Converting LIT books to modern formats

• E-book preservation and archival

• DRM-free LIT file extraction

Advantages

• Rich text formatting

• Image and multimedia support

• Chapter navigation

• Annotation support

Limitations

• Obsolete format (Microsoft Reader discontinued)

• May include DRM (not supported by Cabriolet)

• Limited to e-book content

• Complex format requiring specialized handling

OAB (Offline Address Book)

Purpose and History

OAB files are used by Microsoft Outlook to store compressed copies of the Global Address List for offline use.

Technical Characteristics

• File Extension: .oab

• Magic Bytes: Format-specific header

• Structure: Compressed data blocks

• Compression: LZ-based compression

• Content: Address book entries and metadata

When to Use OAB

• Extracting Outlook address book data

• Migrating email contact information

• Offline address book analysis

• Email system forensics

Advantages

• Efficient storage of contact data

• Fast decompression

• Structured data format

• Good compression for text data

Limitations

• Specialized format for Outlook only

• Limited general-purpose use

• Requires understanding of address book structure

• May require additional parsing of decompressed data

SZDD (Single File Compression)

Purpose and History

SZDD is one of Microsoft’s earliest compression formats, using LZSS compression. It was commonly used for compressing individual files in Windows 3.x distributions.

Technical Characteristics

• File Extension: Often .?? (third character changed to )

• Magic Bytes: SZDD (0x535A4444)

• Structure: Simple header + compressed data

• Compression: LZSS algorithm exclusively

• Header: Contains original filename character

When to Use SZDD

• Legacy Windows 3.x file decompression

• Simple single-file compression

• Converting old compressed files

• Archival of historical software

Advantages

• Very simple format

• Fast decompression

• Small overhead

• Reliable for text files

Limitations

• Single file only

• LZSS compression only (moderate ratios)

• Minimal metadata

• Obsolete format

Features Matrix

Compression Algorithm Support

Algorithm	CAB	CHM	HLP	KWAJ	LIT	OAB	SZDD
None (Store)	✓
LZSS				✓			✓
MSZIP (Deflate)	✓			✓
Quantum	✓			✓
LZX	✓	✓
LZ77			✓			✓
DES + LZ					✓

Feature Support Matrix

Feature	CAB	CHM	HLP	KWAJ	LIT	OAB	SZDD
Multi-file archives	✓	✓	✓		✓	✓
Folder hierarchy	✓	✓	✓		✓
File attributes	✓	~		~		~	~
Timestamps	✓			✓			✓
Metadata	✓	✓	~	~	✓	~
Digital signatures	✓
Spanning/Multi-volume	✓
Embedded archives	✓	✓
Encryption/DRM	~				✓
Full-text search		✓	✓

Legend: ✓ = Full support, ~ = Partial support, (blank) = Not supported

Use case recommendations

Software Distribution

Recommended: CAB

• Multi-file support with folders

• Excellent compression ratios

• Digital signature support

• Industry standard for Windows installers

• Multi-volume support for large distributions

Alternative: KWAJ (single files only)

Documentation and Help

Recommended: CHM

• Rich HTML content support

• Built-in search and navigation

• Excellent for technical documentation

• Native Windows integration

Alternative: HLP (legacy systems only)

Single File Compression

Recommended: KWAJ or SZDD

• Simple single-file format

• Preserves original filename (KWAJ)

• Fast compression/decompression

• Good for distribution of individual files

E-book Management

Recommended: LIT

• Only option for Microsoft Reader books

• Suitable for DRM-free e-books

• Convert to modern formats (EPUB, MOBI)

Outlook Data Extraction

Recommended: OAB

• Only format for Outlook address books

• Efficient storage and retrieval

• Specialized for contact data

Legacy System Support

Recommended: Depends on era

• Windows 3.x: SZDD, HLP

• Windows 95/98: CAB, HLP

• Windows 2000/XP: CAB, CHM

• Modern: CAB, CHM

Performance Characteristics

Compression Ratio Comparison

Based on typical use cases (higher is better):

Format	Text Files	Binary Files
CAB (LZX)	85-90%	60-75%
CAB (MSZIP)	70-80%	50-65%
CAB (Quantum)	75-85%	55-70%
CHM (LZX)	85-90%	N/A
HLP (LZ77)	65-75%	N/A
KWAJ (MSZIP)	70-80%	50-65%
LIT (DES+LZ)	70-80%	N/A
OAB (LZ)	65-75%	55-65%
SZDD (LZSS)	55-70%	40-55%

Decompression Speed Comparison

Relative speed on typical hardware (higher is better):

• Very Fast: SZDD, OAB

• Fast: HLP, KWAJ, CAB (MSZIP)

• Moderate: CAB (LZX), CAB (Quantum), CHM

• Slow: LIT (due to encryption)

Memory Requirements

Approximate memory usage during decompression:

• Low (< 1MB): SZDD, KWAJ, OAB

• Moderate (1-8MB): CAB (MSZIP), HLP

• High (8-32MB): CAB (LZX), CAB (Quantum), CHM

• Variable: LIT (depends on e-book size)

Interoperability Notes

Cross-platform Support

Format	Windows	macOS/Linux	Web Browsers
CAB	Native	Via tools	Limited
CHM	Native	Third-party	No
HLP	Legacy only	Third-party	No
KWAJ	Via tools	Via tools	No
LIT	Via tools	Via tools	No
OAB	Via Outlook	Via tools	No
SZDD	Via tools	Via tools	No

Format Conversion Paths

Common conversion scenarios:

• HLP → CHM: Modernize help files

• LIT → EPUB: Convert e-books to modern format

• CAB → ZIP: Create cross-platform archives

• SZDD/KWAJ → Uncompressed: Extract for modern use

• OAB → CSV/vCard: Export contact data

Historical Context and Evolution

Timeline

• Early 1990s: SZDD, HLP introduced with Windows 3.x

• Mid 1990s: CAB format debuts with Windows 95

• Late 1990s: CHM replaces HLP, OAB for Outlook

• Early 2000s: LIT format for Microsoft Reader

• Present: CAB and CHM remain in active use, others legacy

Format Evolution

The progression shows Microsoft’s changing priorities:

1. Simplicity (SZDD): Basic single-file compression

2. Sophistication (CAB): Multi-file, multi-algorithm archives

3. Specialization (CHM, OAB, LIT): Purpose-built formats

4. Consolidation: Modern Windows uses primarily CAB and CHM

Format Selection Guide

Decision tree

Need to compress files?
├── Single file?
│   ├── Legacy Windows 3.x? → SZDD
│   ├── Need metadata? → KWAJ
│   └── Modern system? → Use ZIP/7z instead
├── Multiple files?
│   ├── Help documentation?
│   │   ├── HTML-based? → CHM
│   │   └── Legacy? → HLP
│   ├── E-book content? → LIT
│   ├── Outlook data? → OAB
│   └── Software distribution? → CAB
└── Archive or read existing files? → Use appropriate format

Best practices

1. For new projects: Use standard formats (ZIP, 7z) unless Windows-specific features required

2. For Windows installers: Use CAB with LZX compression

3. For documentation: Use CHM for Windows-only, HTML for cross-platform

4. For legacy support: Maintain tools for reading old formats

5. For archival: Convert to modern formats when possible

Further reading

• CAB Format Guide

• CHM Format Guide

• HLP Format Guide

• KWAJ Format Guide

• LIT Format Guide

• OAB Format Guide

• SZDD Format Guide

• Choosing Compression Algorithm

• Performance Benchmarks

See also

• Format Guides

• Compression Algorithms

• Basic Usage