This format is basically a raw one. There is just one band per files, except in the RGB24 data type where the Red, Green and Blue bands are store interleafed by pixels in the order Blue, Green and Red. The others data type are unsigned 8 bits integer with values from 0 to 255 or signed 16 bits integer with values from -32.768 to 32.767 or 32 bits single precision floating point.32 bits. The description of the file is stored in a companying text file, extension RDC.
The RDC image description file doesn't include color table, or detailed geographic referencing information. The color table if present can be obtained by another companying file using the same base name as the RST file and SMP as extension.
For geographical referencing identification, the RDC file contains information that points to a file that holds the geographic reference details. Those files uses extension REF and resides in the same folder as the RST image or more likely in the Idrisi installation folders.
Therefore the presence or absence of the Idrisi software in the running operation system will determine the way that this driver will work. By setting the environment variable IDRISIDIR pointing to the Idrisi main installation folder will enable GDAL to find more detailed information about geographical reference and projection in the REF files.
Note that the RST driver recognizes the name convention used in Idrisi for UTM and State Plane geographic reference so it doesn't need to access the REF files. That is the case for RDC file that specify "utm-30n" or "spc87ma1" in the "ref. system" field. Note that exporting to RST in any other geographical reference system will generate a suggested REF content in the comment section of the RDC file.