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<!DOCTYPE document PUBLIC "-//APACHE//DTD Documentation V1.1//EN" "../dtd/document-v11.dtd">
<document>
  <header>
    <title>POIFS File System Internals</title>
    <authors>
      <person email="mjohnson@apache.org" name="Marc Johnson" id="MJ"/>
    </authors>
  </header>
  <body>
    <section><title>POIFS File System Internals</title>
      <section><title>Introduction</title>
        <p>POIFS file systems are essentially normal files stored on a
           Java-compatible platform's native file system. They are
           typically identified by names ending in a four character
           extension noting what type of data they contain. For
           example, a file ending in &quot;.xls&quot; would likely
           contain spreadsheet data, and a file ending in
           &quot;.doc&quot; would probably contain a word processing
           document. POIFS file systems are called &quot;file
           system&quot;, because they contain multiple embedded files
           in a manner similar to traditional file systems. Along
           functional lines, it would be more accurate to call these
           POIFS archives. For the remainder of this document it is
           referred to as a file system in order to avoid confusion
           with the &quot;files&quot; it contains.</p>
        <p>POIFS file systems are compatible with those document
           formats used by a well-known software company's popular
           office productivity suite and programs outputting
           compatible data. Because the POIFS file system does not
           provide compression, encryption or any other worthwhile
           feature, its not a good choice unless you require
           interoperability with these programs.</p>
        <p>The POIFS file system does not encode the documents
           themselves. For example, if you had a word processor file
           with the extension &quot;.doc&quot;, you would actually
           have a POIFS file system with a document file archived
           inside of that file system.</p>
      </section>
      <section><title>Document Conventions</title>
        <p>This document utilizes the numeric types as described by
           the Java Language Specification, which can be found at
           <link href="http://java.sun.com">http://java.sun.com</link>. In
           short:</p>
        <ul>
          <li>A <em>byte</em> is an 8 bit signed integer ranging from
              -128 to 127.</li>
          <li>A <em>short</em> is a 16 bit signed integer ranging from
              -32768 to 32767</li>
          <li>An <em>int</em> is a 32 bit signed integer ranging from
              -2147483648 to 2147483647</li>
          <li>A <em>long</em> is a 64 bit signed integer ranging from
              -9.22E18 to 9.22E18.</li>
        </ul>
        <p>The Java Language Specification spells out a number of
           other types that are not referred to by this document.</p>
        <p>Where this document makes references to &quot;endian
           conversion&quot; it is referring to the byte order of
           stored numbers. Numbers in &quot;little-endian order&quot;
           are stored with the <em>least</em> significant byte first. In
           order to properly read a short, for example, you'd read two
           bytes and then shift the second byte 8 bits to the left
           before performing an <code>or</code> operation to it
           against the first byte. The following code illustrates this
           method:</p>
	<source>
public int getShort (byte[] rec)
{
    return ((rec[1] &lt;&lt; 8) | (rec[0] &amp; 0x00ff));
}</source>
      </section>
      <section><title>File System Walkthrough</title>
        <p>This is a walkthrough of a POIFS file system and how it is
           put together. It is not intended to give a concise
           description but to give a &quot;big picture&quot; of the
           general structure and how it's interpreted.</p>
        <p>A POIFS file system begins with a header. This header
           identifies locations in the file by function and provides a
           sanity check identifying a file as a POIFS file system.</p>
        <p>The first 64 bits of the header compose a <em>magic number
           identifier.</em> This identifier tells the client software
           that this is indeed a POIFS file system and that it should
           be treated as such. This is a &quot;sanity check&quot; to
           make sure this is a POIFS file system and not some other
           format. The header also contains an <em>array of block
           numbers</em>. These block numbers refer to blocks in the
           file. When these blocks are read together they form the
           <em>Block Allocation Table</em>. The header also contains a
           pointer to the first element in the <em>property table</em>,
           also known as the <em>root element</em>, and a pointer to the
           <em>small Block Allocation Table (SBAT)</em>.</p>
        <p>The <em>block allocation table</em> or <em>BAT</em>, along with
           the <em>property table</em>, specify which blocks in the file
           system belong to which files. After the header block, the
           file system is divided into identically sized blocks of
           data, numbered from 0 to however many blocks there are in
           the file system. For each file in the file system, its
           entry in the property table includes the index of the first
           block in the array of blocks. Each block's index into the
           array of blocks is also its index into the BAT, and the
           integer value stored at that index in the BAT gives the
           index of the next block in the array (and thus the index of
           the next BAT value). A special value is stored in the BAT
           to indicate &quot;end of file&quot;.</p>
        <p>The <em>property table</em> is essentially the directory
           storage for the file system. It consists of the name of the
           file or directory, its <em>start block</em> in both the file
           system and <em>BAT</em>, and its actual size. The first
           property in the property table is the <em>root
           element</em>. It has two purposes: to be a directory entry
           (the root of the directory tree, to be specific), and to
           hold the start block for the <em>small block data</em>.</p>
	<p>Small block data is a special file that contains the data
	   for small files (less than 4K bytes). It subdivides its
	   blocks into smaller blocks and there is a special small
	   block allocation table that, like the main BAT for larger
	   files, is used to map a small file to its small blocks.</p>
      </section>
	<section><title>Header Block</title>
          <p>The POIFS file system begins with a <em>header
             block</em>. The first 64 bits of the header form a long
             <em>file type id</em> or <em>magic number identifier</em> of
             <code>0xE11AB1A1E011CFD0L</code>. This is basically a
             sanity check. If this isn't the first thing in the header
             (and consequently the file system) then this is not a
             POIFS file system and should be read with some other
             library.</p>
          <p>It's important to know the most important parts of the
             header. These are discussed in the rest of this
             section.</p>
	  <section><title>BATs</title>
            <p>At offset <em>0x2C</em> is an int specifying the number
               of elements in the <em>BAT array</em>. The array at
               <em>0x4C</em> an array of ints. This array contains the
               indices of every block in the Block Allocation
               Table.</p>
	  </section>
	  <section><title>XBATs</title>
	    <p>Very large POIFS archives may have more blocks than can
               be addressed by the BAT blocks enumerated in the header
               block. How large? Well, the BAT array in the header can
               contain up to 109 BAT block indices; each BAT block
               references up to 128 blocks, and each block is 512
               bytes, so we're talking about 109 * 128 * 512 =
               6.8MB. That's a pretty respectable document! But, you
               could have much more data than that, and in today's
               world of cheap gigabyte drives, why not? So, the BAT
               may be extended in that event. The integer value at
               offset <em>0x44</em> of the header is the index of the
               first <em>extended BAT (XBAT) block</em>. At offset
               <em>0x48</em> of the header, there is an int value that
               specifies how many XBAT blocks there are. The XBAT
               blocks begin at the specified index into the array of
               blocks making up the POIFS file system, and continue in
               sequence for the specified count of XBAT blocks.</p>
            <p>Each XBAT block contains the indices of up to 128 BAT
               blocks, so the document size can be expanded by another
               8MB for each XBAT block. The BAT blocks indexed by an
               XBAT block are appended to the end of the list of BAT
               blocks enumerated in the header block. Thus the BAT
               blocks enumerated in the header block are BAT blocks 0
               through 108, the BAT blocks enumerated in the first
               XBAT block are BAT blocks 109 through 236, the BAT
               blocks enumerated in the second XBAT block are BAT
               blocks 237 through 364, and so on.</p>
	    <p>Through the use of XBAT blocks, the limit on the
	       overall document size is that imposed by the 4-byte
	       block indices; if the indices are unsigned ints, the
	       maximum file size is 2 terabytes, 1 terabyte if the
	       indices are treated as signed ints. Either way, I have
	       yet to see a disk drive large enough to accommodate
	       such a file on the shelves at the local office supply
	       stores.</p>
	  </section>
	  <section><title>SBATs</title>
            <p>If a file contained in a POIFS archive is smaller than
               4096 bytes, it is stored in small blocks. Small blocks
               are 64 bytes in length and are contained within big
               blocks, up to 8 to a big block. As the main BAT is used
               to navigate the array of big blocks, so the <em>small
               block allocation table</em> is used to navigate the
               array of small blocks. The SBAT's start block index is
               found at offset <em>0x3C</em> of the header block, and
               remaining blocks constituting the SBAT are found by
               walking the main BAT as if it were an ordinary file in
               the POIFS file system (this process is described
               below).</p>
	  </section>
	  <section><title>Property Table Start Index</title>
            <p>An integer at address <em>0x30</em> specifies the start
               index of the property table. This integer is specified
               as a <em>&quot;block index&quot;</em>. The Property Table
               is stored, as is almost everything in a POIFS file
               system, in big blocks and walked via the BAT. The
               Property Table is described below.</p>
	  </section>
	</section>
	<section><title>Property Table</title>
          <p>The property table is essentially nothing more than the
             directory system. Properties are 128 byte records
             contained within the 512 byte blocks. The first property
             is always the Root Entry. The following applies to
             individual properties within a property table:</p>
	  <ul>
	    <li>At offset <em>0x00</em> in the property is the
                &quot;<em>name</em>&quot;. This is stored as an
                uncompressed 16 bit unicode string. In short every
                other byte corresponds to an &quot;ASCII&quot;
                character. The size of this string is stored at offset
                <em>0x40</em> (<em>string size</em>) as a short.</li>
            <li>At offset <em>0x42</em> is the <em>property type</em>
                (byte). The type is 1 for directory, 2 for file or 5
                for the Root Entry.</li>
	    <li>At offset <em>0x43</em> is the <em>node color</em>
                (byte). The color is either 1, (black), or 0,
                (red). Properties are apparently meant to be arranged
                in a red-black binary tree, subject to the following
                rules:
	      <ol>
	        <li>The root of the tree is always black</li>
		<li>Two consecutive nodes cannot both be red</li>
		<li>A property is less than another property if its
		    name length is less than the other property's name
		    length</li>
		<li>If two properties have the same name length, the
		    sort order is determined by the sort order of the
		    properties' names.</li>
	      </ol></li>
	    <li>At offset <em>0x44</em> is the index (int) of the
	        <em>previous property</em>.</li>
	    <li>At offset <em>0x48</em> is the index (int) of the
                <em>next property</em>.</li>
            <li>At offset <em>0x4C</em> is the index (int) of the
                <em>first directory entry</em>. This is used by
                directory entries.</li>
	    <li>At offset <em>0x74</em> is an integer giving the
                <em>start block</em> for the file described by this
                property. This index corresponds to an index in the
                array of indices that is the Block Allocation Table
                (or the Small Block Allocation Table) as well as the
                index of the first block in the file. This is used by
                files and the root entry.</li>
	    <li>At offset <em>0x78</em> is an integer giving the total
                <em>actual size</em> of the file pointed at by this
                property. If the file size is less than 4096, the file
                is stored in small blocks and the SBAT is used to walk
                the small blocks making up the file. If the file size
                is 4096 or larger, the file is stored in big blocks
                and the main BAT is used to walk the big blocks making
                up the file. The exception to this rule is the <em>Root
                Entry</em>, which, regardless of its size, is
                <em>always</em> stored in big blocks and the main BAT is
                used to walk the big blocks making up this special
                file.</li>
	  </ul>
	</section>
	<section><title>Root Entry</title>
          <p>The <em>Root Entry</em> in the <em>Property Table</em>
             contains the information necessary to read and write
             small files, which are files less than 4096 bytes
             long. The start block field of the Root Entry is the
             start index of the <em>Small Block Array</em>, which is
             read like any other file in the POIFS file system. Since
             the SBAT cannot be used without the Small Block Array,
             the Root Entry MUST be read or written using the <em>Block
             Allocation Table</em>. The blocks making up the Small
             Block Array are divided into 64-byte small blocks, up to
             the size indicated in the Root Entry (which should always
             be a multiple of 64).</p>
	</section>
	<section><title>Walking the Nodes of the Property Table</title>
          <p>The individual properties form a directory tree, with the
             <em>Root Entry</em> as the directory tree's root, as shown
             in the accompanying drawing. Note the numbers in
             parentheses in each node; they represent the node's index
             in the array of properties. The <em>NEXT_PROP</em>,
             <em>PREVIOUS_PROP</em>, and <em>CHILD_PROP</em> fields hold
             these indices, and are used to navigate the tree.</p>
          <p><img alt="property set" src="images/PropertySet.jpg" /></p>
	  <p>Each directory entry (i.e., a property whose type is
             <em>directory</em> or <em>root entry</em>) uses its
             <em>CHILD_PROP</em> field to point to one of its
             subordinate (child) properties. It doesn't seem to matter
             which of its children it points to. Thus in the previous
             drawing, the Root Entry's CHILD_PROP field may contain 1,
             4, or the index of one of its other children.  Similarly,
             the directory node (index 1) may have, in its CHILD_PROP
             field, 2, 3, or the index of one of its other
             children.</p>
          <p>The children of a given directory property point to each
             other in a similar fashion by using their
             <em>NEXT_PROP</em> and <em>PREVIOUS_PROP</em> fields.</p>
	  <p>Unused <em>NEXT_PROP</em>, <em>PREVIOUS_PROP</em>, and
             <em>CHILD_PROP</em> fields contain the marker value of
             -1. All file properties have a value of -1 for their
             CHILD_PROP fields for example.</p>
	</section>
	<section><title>Block Allocation Table</title>
	  <p>The <em>BAT blocks</em> are pointed at by the bat array
             contained in the header and supplemented, if necessary,
             by the <em>XBAT blocks</em>. These blocks form a large
             table of integers. These integers are block numbers. The
             <em>Block Allocation Table</em> holds chains of integers.
             These chains are terminated with -2. The elements in
             these chains refer to blocks in the files. The starting
             block of a file is NOT specified in the BAT.  It is
             specified by the <em>property</em> for a given file. The
             elements in this BAT are both the block number (within
             the file minus the header) <em>and</em> the number of the
             next BAT element in the chain. This can be thought of as
             a linked list of blocks. The BAT array contains the links
             from one block to the next, including the end of chain
             marker.</p>
          <p>Here's an example: Let's assume that the BAT begins as
             follows:</p>
	  <p><code>BAT[ 0 ] = 2</code></p>
	  <p><code>BAT[ 1 ] = 5</code></p>
	  <p><code>BAT[ 2 ] = 3</code></p>
	  <p><code>BAT[ 3 ] = 4</code></p>
	  <p><code>BAT[ 4 ] = 6</code></p>
	  <p><code>BAT[ 5 ] = -2</code></p>
	  <p><code>BAT[ 6 ] = 7</code></p>
	  <p><code>BAT[ 7 ] = -2</code></p>
	  <p><code>...</code></p>
	  <p>Now, if we have a file whose Property Table entry says it
             begins with index 0, we walk the BAT array and see that
             the file consists of blocks 0 (because the start block is
             0), 2 (because BAT[ 0 ] is 2), 3 (BAT[ 2 ] is 3), 4 (BAT[
             3 ] is 4), 6 (BAT[ 4 ] is 6), and 7 (BAT[ 6 ] is 7). It
             ends at block 7 because BAT[ 7 ] is -2, which is the end
             of chain marker.</p>
          <p>Similarly, a file beginning at index 1 consists of
             blocks 1 and 5.</p>
	  <p>Other special numbers in a BAT array are:</p>
          <ul>
            <li>-1, which indicates an unused block</li>
            <li>-3, which indicates a &quot;special&quot; block, such
                as a block used to make up the Small Block Array, the
                Property Table, the main BAT, or the SBAT</li>
          </ul>
	</section>
      <section><title>File System Structures</title>
        <p>The following outlines the basic file system structures.</p>
	<section><title>Header (block 1) -- 512 (0x200) bytes</title>
          <table>
	    <tr>
	      <td><em>Field</em></td>
	      <td><em>Description</em></td>
	      <td><em>Offset</em></td>
	      <td><em>Length</em></td>
	      <td><em>Default value or const</em></td>
	    </tr>
            <tr>
	      <td>FILETYPE</td>
	      <td>Magic number identifying this as a POIFS file
	          system.</td>
	      <td>0x0000</td>
	      <td>Long</td>
	      <td>0xE11AB1A1E011CFD0</td>
	    </tr>
            <tr>
	      <td>UK1</td>
	      <td>Unknown constant</td>
	      <td>0x0008</td>
	      <td>Integer</td>
	      <td>0</td>
	    </tr>
            <tr>
	      <td>UK2</td>
	      <td>Unknown Constant</td>
	      <td>0x000C</td>
	      <td>Integer</td>
	      <td>0</td>
	    </tr>
            <tr>
	      <td>UK3</td>
	      <td>Unknown Constant</td>
	      <td>0x0014</td>
	      <td>Integer</td>
	      <td>0</td>
	    </tr>
            <tr>
	      <td>UK4</td>
	      <td>Unknown Constant (revision?)</td>
	      <td>0x0018</td>
	      <td>Short</td>
	      <td>0x003B</td>
	    </tr>
            <tr>
	      <td>UK5</td>
	      <td>Unknown Constant (version?)</td>
	      <td>0x001A</td>
	      <td>Short</td>
	      <td>0x0003</td>
	    </tr>
            <tr>
	      <td>UK6</td>
	      <td>Unknown Constant</td>
	      <td>0x001C</td>
	      <td>Short</td>
	      <td>-2</td>
	    </tr>
            <tr>
	      <td>LOG_2_BIG_BLOCK_SIZE</td>
	      <td>Log, base 2, of the big block size</td>
	      <td>0x001E</td>
	      <td>Short</td>
	      <td>9 (2 ^ 9 = 512 bytes)</td>
	    </tr>
            <tr>
	      <td>LOG_2_SMALL_BLOCK_SIZE</td>
	      <td>Log, base 2, of the small block size</td>
	      <td>0x0020</td>
	      <td>Integer</td>
	      <td>6 (2 ^ 6 = 64 bytes)</td>
	    </tr>
            <tr>
	      <td>UK7</td>
	      <td>Unknown Constant</td>
	      <td>0x0024</td>
	      <td>Integer</td>
	      <td>0</td>
	    </tr>
            <tr>
	      <td>UK8</td>
	      <td>Unknown Constant</td>
	      <td>0x0028</td>
	      <td>Integer</td>
	      <td>0</td>
	    </tr>
            <tr>
	      <td>BAT_COUNT</td>
	      <td>Number of elements in the BAT array</td>
	      <td>0x002C</td>
	      <td>Integer</td>
	      <td>required</td>
	    </tr>
	    <tr>
	      <td>PROPERTIES_START</td>
	      <td>Block index of the first block of the property
	          table</td>
	      <td>0x0030</td>
	      <td>Integer</td>
	      <td>required</td>
	    </tr>
            <tr>
	      <td>UK9</td>
	      <td>Unknown Constant</td>
	      <td>0x0034</td>
	      <td>Integer</td>
	      <td>0</td>
	    </tr>
            <tr>
	      <td>UK10</td>
	      <td>Unknown Constant</td>
	      <td>0x0038</td>
	      <td>Integer</td>
	      <td>0x00001000</td>
	    </tr>
	    <tr>
	      <td>SBAT_START</td>
	      <td>Block index of first big block containing the small
	          block allocation table (SBAT)</td>
	      <td>0x003C</td>
	      <td>Integer</td>
	      <td>-2</td>
	    </tr>
            <tr>
	      <td>SBAT_Block_Count</td>
	      <td>Number of big blocks holding the SBAT</td>
	      <td>0x0040</td>
	      <td>Integer</td>
	      <td>1</td>
	    </tr>
            <tr>
	      <td>XBAT_START</td>
	      <td>Block index of the first block in the Extended Block
	          Allocation Table (XBAT)</td>
	      <td>0x0044</td>
	      <td>Integer</td>
	      <td>-2</td>
	    </tr>
            <tr>
	      <td>XBAT_COUNT</td>
	      <td>Number of elements in the Extended Block Allocation
	          Table (to be added to the BAT)</td>
	      <td>0x0048</td>
	      <td>Integer</td>
	      <td>0</td>
	    </tr>
            <tr>
	      <td>BAT_ARRAY</td>
	      <td>Array of block indices constituting the Block
	          Allocation Table (BAT)</td>
	      <td>0x004C, 0x0050, 0x0054 ... 0x01FC</td>
	      <td>Integer[]</td>
	      <td>-1 for unused elements, at least first element must
	          be filled.</td>
	    </tr>
            <tr>
	      <td>N/A</td>
      	      <td>Header block data not otherwise described in this
	          table</td>
	      <td>N/A</td>
	      <td>N/A</td>
	      <td>-1</td>
	    </tr>
          </table>
	</section>
          <section>
              <title>Block Allocation Table Block -- 512 (0x200) bytes</title>
              <table>
                  <tr>
                      <td>
                          <em>Field</em>
                      </td>
                      <td>
                          <em>Description</em>
                      </td>
                      <td>
                          <em>Offset</em>
                      </td>
                      <td>
                          <em>Length</em>
                      </td>
                      <td>
                          <em>Default value or const</em>
                      </td>
                  </tr>
                  <tr>
                      <td>BAT_ELEMENT</td>
                      <td>Any given element in the BAT block</td>
                      <td>0x0000, 0x0004, 0x0008, ... 0x01FC</td>
                      <td>Integer</td>
                      <td>
                          -1 = unused<br/>
                          -2 = end of chain<br/>
                          -3 = special (e.g., BAT block)<br/>
                          All other values point to the next element in the
                          chain and the next index of a block composing the
                          file.
                      </td>
                  </tr>
              </table>
          </section>
	<section><title>Property Block -- 512 (0x200) byte block</title>
          <table>
	    <tr>
	      <td><em>Field</em></td>
	      <td><em>Description</em></td>
	      <td><em>Offset</em></td>
	      <td><em>Length</em></td>
	      <td><em>Default value or const</em></td>
	    </tr>
            <tr>
	      <td>Properties[]</td>
	      <td>This block contains the properties.</td>
	      <td>0x0000, 0x0080, 0x0100, 0x0180</td>
	      <td>128 bytes</td>
	      <td>All unused space is set to -1.</td>
	    </tr>
          </table>
	</section>
	<section><title>Property -- 128 (0x80) byte block</title>
          <table>
	    <tr>
	      <td><em>Field</em></td>
	      <td><em>Description</em></td>
	      <td><em>Offset</em></td>
	      <td><em>Length</em></td>
	      <td><em>Default value or const</em></td>
	    </tr>
            <tr>
	      <td>NAME</td>
	      <td>A unicode null-terminated uncompressed 16bit string
	          (lose the high bytes) containing the name of the
	          property.</td>
	      <td>0x00, 0x02, 0x04, ... 0x3E</td>
	      <td>Short[]</td>
	      <td>0x0000 for unused elements, field required, 32
	          (0x40) element max</td>
	    </tr>
            <tr>
	      <td>NAME_SIZE</td>
	      <td>Number of characters in the NAME field</td>
	      <td>0x40</td>
	      <td>Short</td>
	      <td>Required</td>
	    </tr>
	    <tr>
	      <td>PROPERTY_TYPE</td>
	      <td>Property type (directory, file, or root)</td>
	      <td>0x42</td>
	      <td>Byte</td>
	      <td>1 (directory), 2 (file), or 5 (root entry)</td>
	    </tr>
            <tr>
	      <td>NODE_COLOR</td>
	      <td>Node color</td>
	      <td>0x43</td>
	      <td>Byte</td>
	      <td>0 (red) or 1 (black)</td>
	    </tr>
            <tr>
	      <td>PREVIOUS_PROP</td>
	      <td>Previous property index</td>
	      <td>0x44</td>
	      <td>Integer</td>
	      <td>-1</td>
	    </tr>
            <tr>
	      <td>NEXT_PROP</td>
	      <td>Next property index</td>
	      <td>0x48</td>
	      <td>Integer</td>
	      <td>-1</td>
	    </tr>
            <tr>
	      <td>CHILD_PROP</td>
	      <td>First child property index</td>
	      <td>0x4c</td>
	      <td>Integer</td>
	      <td>-1</td>
	    </tr>
            <tr>
	      <td>SECONDS_1</td>
	      <td>Seconds component of the created timestamp?</td>
	      <td>0x64</td>
	      <td>Integer</td>
	      <td>0</td>
	    </tr>
            <tr>
	      <td>DAYS_1</td>
	      <td>Days component of the created timestamp?</td>
	      <td>0x68</td>
	      <td>Integer</td>
	      <td>0</td>
	    </tr>
            <tr>
	      <td>SECONDS_2</td>
	      <td>Seconds component of the modified timestamp?</td>
	      <td>0x6C</td>
	      <td>Integer</td>
	      <td>0</td>
	    </tr>
            <tr>
	      <td>DAYS_2</td>
	      <td>Days component of the modified timestamp?</td>
	      <td>0x70</td>
	      <td>Integer</td>
	      <td>0</td>
	    </tr>
            <tr>
	      <td>START_BLOCK</td>
	      <td>Starting block of the file, used as the first block
	          in the file and the pointer to the next block from
	          the BAT</td>
	      <td>0x74</td>
	      <td>Integer</td>
	      <td>Required</td>
	    </tr>
            <tr>
	      <td>SIZE</td>
	      <td>Actual size of the file this property points
	          to. (used to truncate the blocks to the real
	          size).</td>
	      <td>0x78</td>
	      <td>Integer</td>
	      <td>0</td>
	    </tr>
          </table>
	</section>
      </section>
    </section>
  </body>
</document>
