The standard defines an IBM-compatible PC DOS file format for storing waveforms, logical events and descriptive data. A set of COMTRADE files for a given event consists of three files with the following extensions: *.DAT file; the data file *.CFG file; the configuration file *.HDR file (optional); the header file

The *.DAT file is the data file that contains the actual data samples of the recorded or simulated event. These are the digital time-tagged samples of the instantaneous values from both the analog and digital channels. The analog channels are generally voltages and currents, while the digital channels are typically the status of relay contacts. Digital channels have only two states: active or inactive, where each are represented by "1" (active) or "0" (inactive).

The structure of the data files is a series of rows and columns, similar to a spreadsheet. Each row represents a time-tagged sample. The number of columns in the data file depends upon the number of analog and digital channels included in the recording. The number of rows depends upon the sampling rate and the length of a record. If all the data values do not fit on the same line, they are continued without carriage return or line feed. The last value in the record is terminated with a carriage return or line feed.

Each row contains a separate column for the sample number, the time from the beginning of the record in microseconds, and one column for each digital and analog channel. For example, a row with six analog channels and one digital channel will have nine columns. Sequential sample rows are separated by carriage returns and line feed characters