Software-defined radio (SDR) is a radio communication system in which certain parts that are typically implemented in hardware, are now instead implemented in software. A basic SDR system may consist of a personal computer with an RF front-end and equipped with a sound card, or other analog-to-digital converter. The signal processing duty is handed over to a general-purpose processor, rather than being done with special-purpose hardware. Such a design produces a radio which can receive and transmit widely different radio protocols based solely on the software used. The most common and important uses of SDR are for military and cell phone services.