LabWindows/CVI

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TDM versus TDMS

TDM versus TDMS

The TDM data model supports the following two file formats:

  • (Windows) TDM—The TDM file format saves the raw data that the measurement hardware acquires and the meta data in separate files. Meta data can be the name and unit of a measurement channel, the name of the test engineer, and other information. The meta data is in the XML format with the .tdm extension. The raw data is in a compact binary format with the .tdx extension.
  • TDM Streaming (TDMS)—The TDMS file format saves both the raw data and the meta data in the binary format in one file with the .tdms extension.
    Note When creating or opening a .tdms file, LabWindows/CVI might automatically create a .tdms_index file. LabWindows/CVI uses the .tdms_index file to speed up random access to the .tdms file. The .tdms_index file is optional in TDMS applications. If you have disk space limitations, configure the TDMS_OpenFileEx function to stop generating this file.

You can use either format to store measurement data. Use the following table to help you decide which file format is more suitable to your application.

TDM TDMS Notes
Cross-Platform Support

The TDM file format supports Windows only. The TDMS file format supports Windows, Linux, and the NI ETS real-time operating systems with the LabWindows/CVI TDM Streaming Library. The TDMS file format has additional support for OS X, VxWorks, and NI Linux Real-Time with the LabVIEW TDMS VIs.
DAQmx Support

Requires DAQmx 9.0 or later.
DIAdem Support

Requires DIAdem 10.0 or later.
LabVIEW Support

Requires LabWindows/CVI 8.2 or later.
Measurement Studio Support

Requires Measurement Studio 8.6 or later.
LabVIEW Toolkit Support

The TDM file format works with the LabVIEW DataFinder Toolkit. The TDMS file format works with the following LabVIEW toolkits and modules:
  • DataFinder Toolkit 1.0 or later
  • LTE Measurement Suite 1.0 or later
  • MathScript RT Module 8.5 or later
  • Simulation Interface Toolkit 4.0 or later
  • Statechart Module 2.0 or later
  • Sound and Vibration Measurement Suite 7.0 or later
Complex Data Support

In addition to supporting all data types that the TDM file format supports, the TDMS file format also supports other data types, such as single-precision and double-precision complex floating-point numbers. Complex data support is currently only available in LabVIEW.
High-Speed Data Streaming Support

LabWindows/CVI includes the TDM Streaming Library that you can use to stream TDMS data at a high speed. However, LabWindows/CVI does not provide such functions for the TDM file format.
Advanced File Operations Support

In addition to the standard TDM Streaming functions, LabWindows/CVI also provides advanced functions, which enable you to stream TDMS data synchronously or asynchronously. However, LabWindows/CVI does not provide such functions for the TDM file format.
Data Subset Removal Support

You cannot use LabWindows/CVI to remove a channel group or channel from a TDMS file. To remove a channel group or channel from a TDM file, you must use the TDM C DLL, available on ni.com.

Related Information

TDM Data Model

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