This SD2IEC, which can be installed internally in the C64, taps the operating voltage and data signals via the supplied adapter board on the CIA chip of the C64, thus no separate serial cable is required, and the serial socket remains free.
The installation is possible in C64-I (“breadbox”) as well as in C64c (flat case), is non-invasive (without drilling holes or soldering, even if the CIA chip is soldered) and can be removed at any time without leaving any residues.
The video is in German however the accompanying website article can be switched to English on their page. You can also buy the parts needed from their store and there are also full PDFs of the manual and installation available there as well.
