Complex sentence: A connection to a personal computer allows the programmer to download software to the BASIC Stamp, which is stored in the onboard non-volatile memory device: it remains programmed until it is erased or reprogrammed, even when the power is removed.
Split into simpler sentences: A connection to a personal computer allows the programmer to download software to the BASIC Stamp, which is stored in the onboard memory device. This memory is nonvolatile: it remains programmed until it is erased or reprogrammed, even when the power is removed.