Chapter 15. Ext2 and Ext3 Data Structures

The previous chapter outlined the concepts behind the design of ExtX, and this chapter describes the various data structures that make up an ExtX file system. It is assumed that you have either read the previous chapter or are reading it in parallel with this one. If you are not interested in learning about the data structures and layout, you can safely skip this chapter.


ExtX uses the superblock to store the basic file system category data. It is located 1,024 bytes from the start of the file system and has 1,024 bytes allocated to it. It has the fields given in Table 15.1.

Table 15.1. Data structure for the ExtX superblock.

Byte Range




Number of inodes in file system


4–7 ...

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