FreeTDS User Guide: A Guide to Installing, Configuring, and Running FreeTDS
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# History of TDS Versions

At first, there was One Version of TDS common to both vendors, but in keeping with the broad history of private ventures, they soon diverged. Each vendor has subsequently brought out different versions, and neither supports the other's flavor. That is to say, each vendor's client libraries use the latest version of TDS offered by that vendor. You can't reliably use Microsoft's libraries to connect to Sybase, or Sybase's libraries to connect to Microsoft. In some cases you'll get a connection, but pretty soon you'll bump into some incompatibility.

Versions of the TDS protocol

TDS 4.2 Sybase and Microsoft

  The version in use at the time of the Sybase/Microsoft split.

TDS 5.0 Sybase

  Introduced for Sybase. Because TDS 5.0 includes negotiated capabilities through which protocol features can be expanded, we are unlikely to see a new TDS version from Sybase.

TDS 7.0 Microsoft

  Introduced for SQL Server 7.0. Includes support for the extended datatypes in SQL Server 7.0 (such as `char`/`varchar` fields of more than 255 characters). It also includes support for Unicode.

TDS 8.0 Microsoft

  Introduced for SQL Server 2000. Includes support for big integer (64-bit `int`) and "variant" datatypes.

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