MBR (Master Boot Record) partition table: JavaScript parsing library

MBR (Master Boot Record) partition table is a traditional way of MS-DOS to partition larger hard disc drives into distinct partitions.

This table is stored in the end of the boot sector (first sector) of the drive, after the bootstrap code. Original DOS 2.0 specification allowed only 4 partitions per disc, but DOS 3.2 introduced concept of "extended partitions", which work as nested extra "boot records" which are pointed to by original ("primary") partitions in MBR.

KS implementation details

License: CC0-1.0

This page hosts a formal specification of MBR (Master Boot Record) partition table using Kaitai Struct. This specification can be automatically translated into a variety of programming languages to get a parsing library.

JavaScript source code to parse MBR (Master Boot Record) partition table

MbrPartitionTable.js

// This is a generated file! Please edit source .ksy file and use kaitai-struct-compiler to rebuild

(function (root, factory) {
  if (typeof define === 'function' && define.amd) {
    define(['kaitai-struct/KaitaiStream'], factory);
  } else if (typeof module === 'object' && module.exports) {
    module.exports = factory(require('kaitai-struct/KaitaiStream'));
  } else {
    root.MbrPartitionTable = factory(root.KaitaiStream);
  }
}(this, function (KaitaiStream) {
/**
 * MBR (Master Boot Record) partition table is a traditional way of
 * MS-DOS to partition larger hard disc drives into distinct
 * partitions.
 * 
 * This table is stored in the end of the boot sector (first sector) of
 * the drive, after the bootstrap code. Original DOS 2.0 specification
 * allowed only 4 partitions per disc, but DOS 3.2 introduced concept
 * of "extended partitions", which work as nested extra "boot records"
 * which are pointed to by original ("primary") partitions in MBR.
 */

var MbrPartitionTable = (function() {
  function MbrPartitionTable(_io, _parent, _root) {
    this._io = _io;
    this._parent = _parent;
    this._root = _root || this;

    this._read();
  }
  MbrPartitionTable.prototype._read = function() {
    this.bootstrapCode = this._io.readBytes(446);
    this.partitions = new Array(4);
    for (var i = 0; i < 4; i++) {
      this.partitions[i] = new PartitionEntry(this._io, this, this._root);
    }
    this.bootSignature = this._io.ensureFixedContents([85, 170]);
  }

  var PartitionEntry = MbrPartitionTable.PartitionEntry = (function() {
    function PartitionEntry(_io, _parent, _root) {
      this._io = _io;
      this._parent = _parent;
      this._root = _root || this;

      this._read();
    }
    PartitionEntry.prototype._read = function() {
      this.status = this._io.readU1();
      this.chsStart = new Chs(this._io, this, this._root);
      this.partitionType = this._io.readU1();
      this.chsEnd = new Chs(this._io, this, this._root);
      this.lbaStart = this._io.readU4le();
      this.numSectors = this._io.readU4le();
    }

    return PartitionEntry;
  })();

  var Chs = MbrPartitionTable.Chs = (function() {
    function Chs(_io, _parent, _root) {
      this._io = _io;
      this._parent = _parent;
      this._root = _root || this;

      this._read();
    }
    Chs.prototype._read = function() {
      this.head = this._io.readU1();
      this.b2 = this._io.readU1();
      this.b3 = this._io.readU1();
    }
    Object.defineProperty(Chs.prototype, 'sector', {
      get: function() {
        if (this._m_sector !== undefined)
          return this._m_sector;
        this._m_sector = (this.b2 & 63);
        return this._m_sector;
      }
    });
    Object.defineProperty(Chs.prototype, 'cylinder', {
      get: function() {
        if (this._m_cylinder !== undefined)
          return this._m_cylinder;
        this._m_cylinder = (this.b3 + ((this.b2 & 192) << 2));
        return this._m_cylinder;
      }
    });

    return Chs;
  })();

  return MbrPartitionTable;
})();
return MbrPartitionTable;
}));