What is the difference between Siemens programming cable USB-PPI and RS232-PPI?

One end of the USB-PPI is a nine-pin head connected to the PPI/MPI interface of the PLC, and the other end is a USB, and a Siemens driver is required. Usually after installing the software such as STEP7.
One end of the Rs232-PPI is connected to the PLC, and the other end is the port of RS232.