Documentation

    Table of Content
    • 3D File Formats
      • 3D File Formats
      • 3D2
      • 3DS
      • 3MF
      • AMF
      • ASE
      • DAE
      • DRC
      • FBX
      • GLB
      • GLTF
      • JRXML
      • JT
      • OBJ
      • PLY
      • PRC
      • RVM
      • STEP
      • U3D
      • VRML
      • X
      • X3D
    • Audio File Formats
      • Audio File Formats
      • AAC
      • FLAC
      • M3U
      • MID
      • MKA
      • MP3
      • OGG
      • RA
      • SDT
      • STAP
      • WAV
    • CAD File Formats
      • CAD File Formats
      • CF2
      • DC3
      • DGN
      • DWF
      • DWFX
      • DWG
      • DWT
      • DXF
      • HPGL
      • IFC
      • IGES
      • IGS
      • JVSG
      • NWC
      • NWD
      • NWF
      • PAT
      • PHJ
      • PLT
      • PSM
      • PSS
      • RVT
      • STL
    • Compression File Formats
      • Compression File Formats
      • 7Z
      • ARC
      • ARJ
      • BZ2
      • DAA
      • GZ
      • RAR
      • TAR
      • ZIM
      • ZIP
    • Database
      • Database File Formats
      • ACCDB
      • ACCDE
      • ACCDT
      • ACCFT
      • BAK
      • BCP
      • DDL
      • DTSX
      • LDF
      • MDB
      • MDF
      • MYI
      • NDF
      • NSF
      • SQL
      • SQLITE
    • EBook File Formats
      • EBook File Formats
      • AZW
      • AZW3
      • EPUB
      • FB2
      • KFX
      • LRF
      • LRS
      • LRX
      • MOBI
      • TR
    • Email File Formats
      • Email File Formats
      • EDB
      • EML
      • EMLX
      • ICS
      • MBOX
      • MSG
      • OFT
      • OST
      • PST
      • TNEF
      • VCF - Virtual Contact File
    • Font
      • Font File Formats
      • CFF
      • CFF2
      • EOT
      • FNT
      • FON
      • JFPROJ
      • OTF
      • PFA
      • PFB
      • PFM
      • SFD
      • TTF
      • WOFF
    • GIS File Formats
      • GIS File Formats
      • E00
      • FileGDB
      • GeoJSON
      • GML
      • GPX
      • KML
      • KMZ
      • OSM
      • SHP
    • Image File Formats
      • Image File Formats
      • APNG
      • AVIF
      • BMP
      • CDR
      • CMX
      • DCM
      • DIB
      • DICOM
      • DJVU
      • DNG
      • EMF
      • EMZ
      • EXIF
      • GIF
      • ICO
      • J2K
      • JP2
      • JPEG
      • JXR
      • ODG
      • OTG
      • PNG
      • PSB
      • PSD
      • SVGZ
      • TGA
      • TIFF
      • VDX
      • VSD
      • VSDM
      • VSDX
      • VSS
      • VSSM
      • VSSX
      • VST
      • VSTM
      • VSTX
      • VSX
      • VTX
      • WEBP
      • WMF
      • WMZ
    • Note Taking File Formats
      • Note Taking File Formats
      • ONE
      • ONETOC2
    • Page Description Language
      • Page Description Language
      • CGM
      • EPS
      • PCL
      • PS
      • SVG
      • SWF
      • TEX
      • XPS
      • XSLFO
    • PDF
      • PDF
      • PDF/A
      • PDF/E
      • PDF/UA
      • PDF/VT
      • PDF/X
    • Presentation File Formats
      • Presentation File Formats
      • ODP
      • OTP
      • POT
      • POTM
      • POTX
      • PPS
      • PPSM
      • PPSX
      • PPT
      • PPTM
      • PPTX
    • Programming
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      • YAML
    • Project Management File Formats
      • Project Management File Formats
      • MPP
      • MPT
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      • XER
    • Spreadsheet File Formats
      • Spreadsheet File Formats
      • CSV
      • DIF
      • ODS
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      • TSV
      • XLAM
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      • XLS
      • XLSB
      • XLSM
      • XLSX
      • XLT
      • XLTM
      • XLTX
    • Video File Formats
      • Video File Formats
      • 3G2
      • 3GP
      • AVI
      • F4V
      • FLV
      • M4V
      • MKV
      • MOV
      • MP4
      • RM
      • RMVB
      • RV
      • SRT
      • VOB
      • WMV
      • Xvid
    • Web File Formats
      • Web File Formats
      • ASP
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      • CHM
      • CSS
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      • JS
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      • MHTML
      • Sass
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      • VDW
      • XAML
      • XHTML
      • XML
      • XOML
      • XSLT
    • Word Processing File Formats
      • Word Processing File Formats
      • DOC
      • DOCM
      • DOCX
      • DOT
      • DOTM
      • DOTX
      • MD
      • ODT
      • OTT
      • RTF
      • TXT

    What's on this Page

      • What is a ZIM file?
      • ZIM File Format Specifications
        • ZIM Header
      • References
    1. Home
    2. Compression File Formats
    3. ZIM

    What is a ZIM file?

    Files with .zim extension are archives created to store Wiki content offline. It is considered as the most suitable open file format for storing Wikipedia on a USB. It stores site contents in a compact format. Its name comes from “Zeno IMproved” which was the earlier Zeno file format. ZIM is maintained by openZIM project which is sponsored by Wikimedia CH, and supported by the Wikimedia Foundation. ZIM files can be opened by applications such as Kiwix and ZIMReader. OpenZIM project has hosted the implementation of ZIM file format on Github for contribution from OpenSource community.

    ZIM File Format Specifications

    ZIM file format was developed on top of Zeno file format and is not backwards compatible. The format specifications of ZIM file format are available online by openZIM for developer’s reference. OpenZIM has provided C++ open source implementation, LibZim, for reading and writing ZIM files.

    ZIM file format uses LZMA2 compression to make the content compact.

    ZIM File Format

    ZIM Header

    A ZIM file starts with a header that is at offset 0. All the constituents are based on little-endian and all the integers are unsigned integers i.e. uint_16, uint_32, uint_64.

    Field NameTypeOffsetLengthDescription
    magicNumberinteger04Magic number to recognise the file format, must be 72173914 (0x44D495A)
    majorVersioninteger42Major version of the ZIM file format (5 or 6)
    minorVersioninteger62Minor version of the ZIM file format
    uuidinteger816unique id of this zim file
    articleCountinteger244total number of articles
    clusterCountinteger284total number of clusters
    urlPtrPosinteger328position of the directory pointerlist ordered by URL
    titlePtrPosinteger408position of the directory pointerlist ordered by Title
    clusterPtrPosinteger488position of the cluster pointer list
    mimeListPosinteger568position of the MIME type list (also header size)
    mainPageinteger644main page or 0xffffffff if no main page
    layoutPageinteger684layout page or 0xffffffffff if no layout page
    checksumPosinteger728pointer to the md5checksum of this file without the checksum itself. This points always 16 bytes before the end of the file.

    References

    • OpenZIM
    • C++ LibZim