DKU-5 has a chip in it to emulate a serial port through the USB connector. This is for phones without native USB connectivity. DKU-5 is used for models without external memory (6100, 3100, 3120, 3200, 3220, 6610, 7210, 7250, 68xx, 6200, 6220).
CA-42 is a replacement cable for DKU-5 cable. Some phones are compatible with both of them, some with just CA-42.
The main differences are three :
- The CA-42 cable consumes less power than the DKU-5 when it is idle.
- The CA-42 cable is not detected by the PC unless the phone is connected to the other end.
- The CA-42 cable can be also used in Operating Systems other than Windows 98/2K/XP, such as Windows CE, Linux and Mac.