Glossary
The Second Extended File System (EXT2)
Block group
Note:
Blocks are clustered into block groups in order to reduce fragmentation and minimise the amount of head seeking when reading a large amount of consecutive data. Information about each block group is kept in a descriptor table stored in the block(s) immediately after the superblock. Two blocks near the start of each group are reserved for the block usage bitmap and the inode usage bitmap which show which blocks and inodes are in use. Since each bitmap is limited to a single block, this means that the maximum size of a block group is 8 times the size of a block.
The block(s) following the bitmaps in each block group are designated as the inode table for that block group and the remainder are the data blocks. The block allocation algorithm attempts to allocate data blocks in the same block group as the inode which contains them.
Superblock
A critical data structure that contains metadata about the file system, such as total blocks, free blocks, and inode information.
Inode (Index node)
A structure that stores metadata about a file, including its size, permissions, ownership, and pointers to data blocks.
Data blocks
A fixed-size unit of storage that holds the actual file contents.
Block bitmap
A map that tracks the allocation status of data blocks, helping manage used and free blocks.
Inode bitmap
A map that tracks the allocation status of inodes, determining which ones are in use.
Directory Entry
A structure that maps filenames to their corresponding inode numbers, enabling file retrieval.