Whereas the first Arduino I/O Boards used an RS-232 connector and associated circuitry to talk to the rest of the world, modern Arduinos use the popular USB. This versatile interface is an industry standard and is maintained by the USB Implementers Forum, Inc. The USB specification and all other information relating to the USB standard can be found at
The changeover from RS-232 to USB was perhaps inevitable. Most modern PCs and laptops have omitted the once-popular RS-232 port in favor of the smaller USB port. USB-to-RS-232 adapters are available to link older Arduino hardware to more recent PCs.
One major advantage of using USB instead of RS-232 is the availability of a regulated 5V ...