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Virtual Filesystems


Disk Filesystems
CD/DVD Filesystems
Network Filesystems
Flash Filesystems

LEAN is a (recursive) backronym that stands for "Lean yet Effective Allocation and Naming" and is an alternative to the FAT filesystem used by the FreeDOS-32 project.



LEAN uses an extent-based allocation algorithm and is designed to use the little-endian byte ordering. There have been a total of 6 versions (at the time of writing) and the changelog for each release can be found in the specification (see link below). LEAN provides the following features (mostly according to the creators of the specification):

  • Supports Unicode long file names (in contrary to FAT long names, patented by Microsoft).
  • Suppports extended attributes (name-value metadata, embedded in files or forks).
  • Requires a small memory footprint and isn't too intensive on the CPU.
  • Fairly easy to implement and to understand.
  • Suitable for both large and small volumes.
  • Hard and symbolic links.
  • POSIX-compatible.

A more detailed overview of the filesystem's actual capabilities:

  • 512-byte allocation unit (conventional sectors)
  • A maximum volume size of 2^63 - 1 sectors
  • A maximum file size of 2^64 - 1 bytes
  • File names of up to 4068 bytes (case sensitive and in UTF-8 format)


The creators of LEAN have a reference implementation and binaries of a LEAN file manager (Windows/Debian/Linux) available on their website. See this page for more information.

See Also

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