src/UserGuide/latest/FileFormat/Format-Versions.md

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# Format Versions

The format version is the byte immediately after the leading magic string:

```text
6-byte magic string "TsFile"
1-byte format version
```

This guide describes `0x04`. The format byte and the project release number serve different
purposes: a release in the 2.x series can use file format v4. The project release label is not
stored in the file header.

Version 4 uses segmented DeviceIDs and stores per-table device-index roots and Table Schemas
in `TsFileMetadata`. Version 3 uses a single-string device identifier and a different footer.
A reader needs the corresponding version's structures to parse either file correctly.

## Reader Dispatch

Read the version before interpreting data markers, then select the encryption mode:

```text
validate leading magic -> read version -> inspect optional encryption header
  -> resolve encryption mode/profile -> parse the matching data/footer grammar
```

If the observed version is unsupported, report that before parsing the data. A familiar marker
or tail magic does not establish that the rest of the file uses the expected layout.

## Compatibility Contract

Within a supported version, a reader also needs the types, codecs, and encryption features used
by the requested data. For example, v4 Page AEAD files have a `0x06` encryption header at offset
`7`, which selects an extended Chunk Header and a Page-body profile. The version byte stays
`0x04`; a v4 reader without this capability must report it as unsupported.

Assigned identifiers keep their meanings. Unknown footer properties have length-delimited keys
and values, so their byte ranges can be consumed. Unknown data markers generally cannot be
skipped because they have no common payload length. [Extensibility](Extensibility.md) explains
these boundaries, and [Encryption](DataPages/Encryption.md) defines the AEAD layout.