/ɛks tɛnˈdɪd/
noun — "Linux filesystem family."
EXT, short for Extended File System, is a series of filesystems primarily used in Linux operating systems. It was designed to improve upon the limitations of early UNIX-like filesystems by introducing features like larger volume support, journaling, and metadata optimization. The family includes EXT2, EXT3, and EXT4, each progressively adding capabilities while maintaining backward compatibility.
Technically, EXT organizes storage into block groups containing inodes, data blocks, and bitmaps that track free and used blocks. Inodes store file metadata, including size, ownership, permissions, timestamps, and pointers to data blocks. The filesystem supports hierarchical directories and symbolic links. Later versions, such as EXT3 and EXT4, implement journaling to record pending changes, which enhances reliability in the event of system crashes. EXT4 introduces extents, larger storage units for contiguous blocks, improving performance for large files, and supports delayed allocation for better fragmentation handling.
Operationally, writing a file on an EXT filesystem involves allocating an inode, assigning data blocks, and updating the block and inode bitmaps. For EXT3 and EXT4, journal entries are first recorded to ensure atomicity of operations. Reading files involves traversing inodes to access data blocks in sequence, with the filesystem translating logical block numbers to physical storage locations using structures like block group tables. Tools like UUID or device identifiers facilitate mounting and managing multiple volumes.
Example of filesystem creation in Linux:
mkfs.ext4 /dev/sdb1
mount /dev/sdb1 /mnt/data
ls -l /mnt/data
This sequence formats a partition as EXT4, mounts it, and lists its contents.
In practice, EXT filesystems are widely used in desktops, servers, embedded Linux systems, and cloud environments due to their stability, robustness, and Linux kernel integration. Administrators benefit from features like journaling, snapshots via LVM integration, and online resizing in EXT4 without unmounting volumes.
Conceptually, EXT is like a well-organized library: inodes act as catalog cards storing metadata, data blocks are the physical pages, and the journal functions as a safety ledger recording ongoing changes to prevent lost work after power failures.
See EXT2, EXT3, EXT4, UUID, FileSystem.