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EFS (Extent File System) was the default file system used by Silicon Graphics for its UNIX operating systems from GL2-W2.4 through IRIX 5.3 and for all "IRIX software distribution CD-ROMs."


EFS was introduced in March of 1986 with GL2-W2.4 to replace the System V/Bell file system created by AT&T. EFS was deprecated in favor of XFS beginning with the introduction of IRIX 5.3 XFS in December of 1994 and later IRIX 6.0.1 XFS in March of 1995 with all subsequent versions of IRIX using XFS.


According to Silicon Graphics' documentation EFS offered "a significant improvement in file handling performance over the System V file system" while also maintaining complete compatibility with the System V file system: EFS "stores groups of blocks (extents) contiguously on the disk" thus reducing the seek time and access overhead required to access a file.


  • Block size: 512-bytes
    • Block 0: unused or contains a bootstrap program
    • Block 1: superblock, contains file system metadata
  • Maximum file system size: 8GB (224 or 16777214 blocks)
  • Maximum individual file size: 2GB
  • Number of fixed-files created by mkfs: 9

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