In this step the SLC datafile is put on disk in a raw (pixel interleaved, 2x2byte signed (short) integer complex) format. (The reason for this step is that we normally work with the SLC images on cdrom, and that we want to have the files on disk to perform operation requiring both the images. It also serves as a common format for different input.)
A few checks are performed regarding the number of lines, which is written in the header of the SLC data file as well as in the leader file. The image is read/written line by line, no data conversion takes place (though a cutout can be made). If you are working on a little endian platform (X86 PC) then the data is converted from big endian (which is the CEOS format).