There are several ways to retain memory functions in electronic systems. The cheapest is a constant power supply dedicated to keeping the clock and memory current. The second is a capacitive storage array which will deplete over time. The third and most expensive is non volatile ram memory. This third operation is cost prohibitive in most consumer electronics arenas. The constant power source is the most common, and economical by far.
The radio, (in this instance) defaulting to a given frequency is the product of an EEPROM chip, (Electrically Erasable Programable Read Only Memory) microchip that is programmed to tune to the given frequency with the application of power. These are the same type chips which tell your electronic controlled engine how to operate when cold before it actually starts sampling external inputs from the various sensors which is of course closed, and open loop operation.
