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{{DISPLAYTITLE:File Format Specification}}
= I. Introduction =

== I.A. This Document ==

== I.B. Changes for HDF5 1.12 ==

== I.C. Changes for HDF5 1.10 ==

= II. Disk Format: Level 0 - File Metadata =

== II.A. Disk Format: Level 0A - Format Signature and Superblock ==

The superblock may begin at certain predefined offsets within the HDF5 file, allowing a block of unspecified content for users to place additional information at the beginning (and end) of the HDF5 file without limiting the HDF5 Library’s ability to manage the objects within the file itself. This feature was designed to accommodate wrapping an HDF5 file in another file format or adding descriptive information to an HDF5 file without requiring the modification of the actual file’s information. The superblock is located by searching for the HDF5 format signature at byte offset 0, byte offset 512, and at successive locations in the file, each a multiple of two of the previous location; in other words, at these byte offsets: 0, 512, 1024, 2048, and so on.

The superblock is composed of the format signature, followed by a superblock version number and information that is specific to each version of the superblock.

Currently, there are four versions of the superblock format:

* Version 0 is the default format.
* Version 1 is the same as version 0 but with the ''"Indexed Storage Internal Node K"'' field for storing non-default B-tree 'K' value.
* Version 2 has some fields eliminated and compressed from superblock format versions 0 and 1. It has added checksum support and superblock extension to store additional superblock metadata.
* Version 3 is the same as version 2 except that the field ''"File Consistency Flags"'' is used for file locking. This format version will enable support for the latest version.

Versions 0 and 1 of the superblock are described below:

{{layout superblock versions 0 and 1}}

{{fields superblock versions 0 and 1}}

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