That new Raspberry Pi 500 computer you just got has a row of 2x20 pin headers on the right side - those are the GPIO (general purpose input/output) pins, and for those of us who like to hack electronics, they are where the real fun lies. By programming the Pi, you can twiddle those pins high or low, send and receive I2C and SPI data, and access the 3V and 5V power rails.