The PCR-100 uses an industry standard RS232 Serial Cable, with a DB9 male on the radio end, and a DB9 female for most computers that have serial ports. Some older computers may require a DB25 female connector instead.
One thing to note regarding RS232 serial cables. They can be quite long, allowing you to mount the radio in an upstairs closet, and run your serial cable, and audio cables all the way down to the basement if desired. This helps to eliminate signal losses encountered by long coax runs for the antenna. Or you could put a small computer upstairs with the radio, and access the radio via your WiFi network.
I haven't heard of anyone using a Serial-to-USB adapter with the Icom PCR-100. Anyone try it?