L293D is a monolithic integrated, high voltage, high current, 4-channel driver.Basically this means using this chip you can use DC motors and power supplies of up to 36 Volts, thats some pretty big motors and the chip can supply a maximum current of 600mA per channel, the L293D chip is also what’s known as a type of H-Bridge. The H-Bridge is typically an electrical circuit that enables a voltage to be applied across a load in either direction to an output, e.g. motor. - 2 interface for 5V Servo connected to the  high-resolution dedicated timer - no jitter! - Can drive 4 DC motors or 2 stepper motors or 2 Servo - Up to 4 bi-directional DC motors with individual 8-bit speed selection - Up to 2 stepper motors (unipolar or bipolar) with single coil, double coil or interleaved stepping. - 4 H-Bridges: per bridge provides 0.6A (1.2A peak current) with thermal protection, can run motors on 4.5V to 36V DC - Pull down resistors keep motors disabled during power-up - reset button - 2 external terminal power interface, for seperate logic/motor supplies - d compatible for  Mega, Diecimila & Duemilanove