These raw data coming from the ROD are sent to IS by the SctApi using the ScanResultWriter.
This is a Serializable, meaning that it can be written to and read from IS using the concrete IS implimentation of the <Sct_IoManager> i.e. the <IoManagerIS>. An alternative implementation, which is used extensively for performance reasons, is to write the data to file using the same method of serialization, but to publish a proxy in IS.
Temporary files are written to the directory given by the environment variable SCT_SCRATCH_DIR. ISProxy writing is done by the <IOManagerISProxy>, but as a proxy it can still be read seamlessly by the <IOManagerIS>.