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+<!-- X-URL: http://step.polymtl.ca/~ldd/ext2fs/ext2fs_6.html -->
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+<!-- This HTML file has been created by texi2html 1.29
+     from ext2fs.texi on 3 August 1994 -->
+
+<TITLE>Analysis of the Ext2fs structure - Bitmaps</TITLE>
+<P>Go to the <A HREF="ext2fs_5.html">previous</A>, <A HREF="ext2fs_7.html">next</A> section.<P>
+<A NAME="IDX22"></A>
+<H1><A NAME="SEC6" HREF="ext2fs_toc.html#SEC6">Bitmaps</A></H1>
+<P>
+The ext2 file system uses bitmaps to keep track of allocated blocks
+and inodes.
+<A NAME="IDX23"></A>
+<A NAME="IDX24"></A>
+<P>
+The blocks bitmap of each group refers to blocks ranging from the first
+block in the group to the last block in the group. To access the bit of
+a precise block, we first have to look for the group the block belongs
+to and then look for the bit of this block in the blocks bitmap
+contained in the group. It it very important to note that the blocks
+bitmap refer in fact to the smallest allocation unit supported by the
+file system: fragments. Since the block size is always a multiple of
+fragment size, when the file system manager allocates a block, it
+actually allocates a multiple number of fragments. This use of the
+blocks bitmap permits to the file system manager to allocate and
+deallocate space on a fragment basis.
+<A NAME="IDX25"></A>
+<A NAME="IDX26"></A>
+<P>
+The inode bitmap of each group refer to inodes ranging from the first
+inode of the group to the last inode of the group. To access the bit of
+a precise inode, we first have to look for the group the inode belongs
+to and then look for the bit of this inode in the inode bitmap contained
+in the group. To obtain the inode information from the inode table, the
+process is the same, except that the final search is in the inode table
+of the group instead of the inode bitmap.
+<P>
+<P>Go to the <A HREF="ext2fs_5.html">previous</A>, <A HREF="ext2fs_7.html">next</A> section.<P>