explanation.txt

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</TR>
<TR><TD WIDTH="43%" VALIGN="TOP">
<FONT SIZE=2><P>Number of FAT copies</FONT></TD>
<TD WIDTH="19%" VALIGN="TOP">
<FONT SIZE=2><P>1</FONT></TD>
<TD WIDTH="38%" VALIGN="TOP">
<FONT SIZE=2><P>2</FONT></TD>
</TR>
<TR><TD WIDTH="43%" VALIGN="TOP">
<FONT SIZE=2><P>Max. root directory entries</FONT></TD>
<TD WIDTH="19%" VALIGN="TOP">
<FONT SIZE=2><P>2</FONT></TD>
<TD WIDTH="38%" VALIGN="TOP">
<FONT SIZE=2><P>512</FONT></TD>
</TR>
<TR><TD WIDTH="43%" VALIGN="TOP">
<FONT SIZE=2><P>Total sectors</FONT></TD>
<TD WIDTH="19%" VALIGN="TOP">
<FONT SIZE=2><P>2</FONT></TD>
<TD WIDTH="38%" VALIGN="TOP">
<FONT SIZE=2><P>0</FONT></TD>
</TR>
<TR><TD WIDTH="43%" VALIGN="TOP">
<FONT SIZE=2><P>Media descriptor</FONT></TD>
<TD WIDTH="19%" VALIGN="TOP">
<FONT SIZE=2><P>1</FONT></TD>
<TD WIDTH="38%" VALIGN="TOP">
<FONT SIZE=2><P>F8</FONT></TD>
</TR>
<TR><TD WIDTH="43%" VALIGN="TOP">
<FONT SIZE=2><P>Sectors per FAT</FONT></TD>
<TD WIDTH="19%" VALIGN="TOP">
<FONT SIZE=2><P>2</FONT></TD>
<TD WIDTH="38%" VALIGN="TOP">
<FONT SIZE=2><P>256</FONT></TD>
</TR>
<TR><TD WIDTH="43%" VALIGN="TOP">
<FONT SIZE=2><P>Sectors per track</FONT></TD>
<TD WIDTH="19%" VALIGN="TOP">
<FONT SIZE=2><P>2</FONT></TD>
<TD WIDTH="38%" VALIGN="TOP">
<FONT SIZE=2><P>63</FONT></TD>
</TR>
<TR><TD WIDTH="43%" VALIGN="TOP">
<FONT SIZE=2><P>No. of sides</FONT></TD>
<TD WIDTH="19%" VALIGN="TOP">
<FONT SIZE=2><P>2</FONT></TD>
<TD WIDTH="38%" VALIGN="TOP">
<FONT SIZE=2><P>255</FONT></TD>
</TR>
<TR><TD WIDTH="43%" VALIGN="TOP">
<FONT SIZE=2><P>Hidden sectors</FONT></TD>
<TD WIDTH="19%" VALIGN="TOP">
<FONT SIZE=2><P>4</FONT></TD>
<TD WIDTH="38%" VALIGN="TOP">
<FONT SIZE=2><P>63</FONT></TD>
</TR>
<TR><TD WIDTH="43%" VALIGN="TOP">
<FONT SIZE=2><P>Huge sectors</FONT></TD>
<TD WIDTH="19%" VALIGN="TOP">
<FONT SIZE=2><P>4</FONT></TD>
<TD WIDTH="38%" VALIGN="TOP">
<FONT SIZE=2><P>1492902</FONT></TD>
</TR>
<TR><TD WIDTH="43%" VALIGN="TOP">
<FONT SIZE=2><P>BIOS drive number</FONT></TD>
<TD WIDTH="19%" VALIGN="TOP">
<FONT SIZE=2><P>1</FONT></TD>
<TD WIDTH="38%" VALIGN="TOP">
<FONT SIZE=2><P>128</FONT></TD>
</TR>
<TR><TD WIDTH="43%" VALIGN="TOP">
<FONT SIZE=2><P>Reserved sectors</FONT></TD>
<TD WIDTH="19%" VALIGN="TOP">
<FONT SIZE=2><P>1</FONT></TD>
<TD WIDTH="38%" VALIGN="TOP">
<FONT SIZE=2><P>1</FONT></TD>
</TR>
<TR><TD WIDTH="43%" VALIGN="TOP">
<FONT SIZE=2><P>Boot signature</FONT></TD>
<TD WIDTH="19%" VALIGN="TOP">
<FONT SIZE=2><P>1</FONT></TD>
<TD WIDTH="38%" VALIGN="TOP">
<FONT SIZE=2><P>41</FONT></TD>
</TR>
<TR><TD WIDTH="43%" VALIGN="TOP">
<FONT SIZE=2><P>Volume ID</FONT></TD>
<TD WIDTH="19%" VALIGN="TOP">
<FONT SIZE=2><P>4</FONT></TD>
<TD WIDTH="38%" VALIGN="TOP">
<FONT SIZE=2><P>4084677574</FONT></TD>
</TR>
<TR><TD WIDTH="43%" VALIGN="TOP">
<FONT SIZE=2><P>Volume label</FONT></TD>
<TD WIDTH="19%" VALIGN="TOP">
<FONT SIZE=2><P>11</FONT></TD>
<TD WIDTH="38%" VALIGN="TOP">
<FONT SIZE=2><P>ICIT</FONT></TD>
</TR>
<TR><TD WIDTH="43%" VALIGN="TOP">
<FONT SIZE=2><P>File system type</FONT></TD>
<TD WIDTH="19%" VALIGN="TOP">
<FONT SIZE=2><P>8</FONT></TD>
<TD WIDTH="38%" VALIGN="TOP">
<FONT SIZE=2><P>FAT16</FONT></TD>
</TR>
</TABLE>

Earlier, the BPB comprised of entries only up to the entry 'Hidden sectors' in Table 1. For example, it didn't contain the 'Volume label' of the disk. This used to get stored as a directory entry in the directory sectors. However, now the BPB has been extended to include entries like 'Volume label, 'Volume ID', 'File system type', etc. The BPB is now called 'Extended BPB'. Whether the boot sector contains BPB or Extended BPB is indicated by the value of the entry 'Boot signature'. If it contains a value 29h then the disk has an Extended BPB.
The 'Volume ID' entry is the serial number that is recorded on the disk while formatting it. This is the same number that is shown when we run the 'Dir' command on the disk.
A 1.44 MB disk supports a 12-bit FAT system. The total number of sectors on this disk is 2880. This value is stored in the entry 'Total Sectors'. There is another entry in the boot parameters called 'Huge Sectors'. For a 12-bit FAT System, this entry has a value 0. For bigger capacity hard disks the value of total number of sectors would be much more than what can be accomodated in the 2-byte entry called 'Total Sectors'. Hence for such disks this entry contains a value 0 and the total number of sectors value is stored in the entry 'Huge Sectors'.
Let us now take a look at the 32-bit FAT system's boot sector contents. These are shown in Table 3.

<TABLE BORDER CELLSPACING=2 CELLPADDING=7 WIDTH=406>
<TR><TD WIDTH="47%" VALIGN="TOP">
<B><FONT SIZE=2><P>Description</B></FONT></TD>
<TD WIDTH="23%" VALIGN="TOP">
<B><FONT SIZE=2><P>Length</B></FONT></TD>
<TD WIDTH="31%" VALIGN="TOP">
<B><FONT SIZE=2><P>Typical Values</B></FONT></TD>
</TR>
<TR><TD WIDTH="47%" VALIGN="TOP">
<FONT SIZE=2><P>Jump instruction</FONT></TD>
<TD WIDTH="23%" VALIGN="TOP">
<FONT SIZE=2><P>3</FONT></TD>
<TD WIDTH="31%" VALIGN="TOP">
<FONT SIZE=2><P>EB5890</FONT></TD>
</TR>
<TR><TD WIDTH="47%" VALIGN="TOP">
<FONT SIZE=2><P>OEM name</FONT></TD>
<TD WIDTH="23%" VALIGN="TOP">
<FONT SIZE=2><P>8</FONT></TD>
<TD WIDTH="31%" VALIGN="TOP">
<FONT SIZE=2><P>MSWIN4.1</FONT></TD>
</TR>
<TR><TD WIDTH="47%" VALIGN="TOP">
<FONT SIZE=2><P>Bytes per sector</FONT></TD>
<TD WIDTH="23%" VALIGN="TOP">
<FONT SIZE=2><P>2</FONT></TD>
<TD WIDTH="31%" VALIGN="TOP">
<FONT SIZE=2><P>512</FONT></TD>
</TR>
<TR><TD WIDTH="47%" VALIGN="TOP">
<FONT SIZE=2><P>Sectors per cluster</FONT></TD>
<TD WIDTH="23%" VALIGN="TOP">
<FONT SIZE=2><P>1</FONT></TD>
<TD WIDTH="31%" VALIGN="TOP">
<FONT SIZE=2><P>8</FONT></TD>
</TR>
<TR><TD WIDTH="47%" VALIGN="TOP">
<FONT SIZE=2><P>Reserved sectors</FONT></TD>
<TD WIDTH="23%" VALIGN="TOP">
<FONT SIZE=2><P>2</FONT></TD>
<TD WIDTH="31%" VALIGN="TOP">
<FONT SIZE=2><P>51</FONT></TD>
</TR>
<TR><TD WIDTH="47%" VALIGN="TOP">
<FONT SIZE=2><P>Number of FAT copies</FONT></TD>
<TD WIDTH="23%" VALIGN="TOP">
<FONT SIZE=2><P>1</FONT></TD>
<TD WIDTH="31%" VALIGN="TOP">
<FONT SIZE=2><P>2</FONT></TD>
</TR>
<TR><TD WIDTH="47%" VALIGN="TOP">
<FONT SIZE=2><P>Root directory entries</FONT></TD>
<TD WIDTH="23%" VALIGN="TOP">
<FONT SIZE=2><P>2</FONT></TD>
<TD WIDTH="31%" VALIGN="TOP">
<FONT SIZE=2><P>0</FONT></TD>
</TR>
<TR><TD WIDTH="47%" VALIGN="TOP">
<FONT SIZE=2><P>Total sectors</FONT></TD>
<TD WIDTH="23%" VALIGN="TOP">
<FONT SIZE=2><P>2</FONT></TD>
<TD WIDTH="31%" VALIGN="TOP">
<FONT SIZE=2><P>0</FONT></TD>
</TR>
<TR><TD WIDTH="47%" VALIGN="TOP">
<FONT SIZE=2><P>Media descriptor</FONT></TD>
<TD WIDTH="23%" VALIGN="TOP">
<FONT SIZE=2><P>1</FONT></TD>
<TD WIDTH="31%" VALIGN="TOP">
<FONT SIZE=2><P>F8</FONT></TD>
</TR>
<TR><TD WIDTH="47%" VALIGN="TOP">
<FONT SIZE=2><P>Sectors per FAT</FONT></TD>
<TD WIDTH="23%" VALIGN="TOP">
<FONT SIZE=2><P>2</FONT></TD>
<TD WIDTH="31%" VALIGN="TOP">
<FONT SIZE=2><P>0</FONT></TD>
</TR>
<TR><TD WIDTH="47%" VALIGN="TOP">
<FONT SIZE=2><P>Sectors per track</FONT></TD>
<TD WIDTH="23%" VALIGN="TOP">
<FONT SIZE=2><P>2</FONT></TD>
<TD WIDTH="31%" VALIGN="TOP">
<FONT SIZE=2><P>63</FONT></TD>
</TR>
<TR><TD WIDTH="47%" VALIGN="TOP">
<FONT SIZE=2><P>No. of sides</FONT></TD>
<TD WIDTH="23%" VALIGN="TOP">
<FONT SIZE=2><P>2</FONT></TD>
<TD WIDTH="31%" VALIGN="TOP">
<FONT SIZE=2><P>255</FONT></TD>
</TR>
<TR><TD WIDTH="47%" VALIGN="TOP">&nbsp;</TD>
<TD WIDTH="23%" VALIGN="TOP">&nbsp;</TD>
<TD WIDTH="31%" VALIGN="TOP">
<I><FONT SIZE=2><P>continued