Arduino is a well-known platform among electronics hobbyists because of its simplicity, robust and intuitive design, and ease of use even for non-electronics enthusiasts. Instead of introducing new PCB variants or different microcontrollers on board, they made some significant upgrades in the Arduino concept. Recent changes came with two new Arduino boards, so-called Uno and Mega2560. Probably the most significant difference is the USB to serial converter. They decided to replace seemed to be hard-positioned FTDI chip FT232RL with microcontroller Atmega8U2 that has a hardware USB interface. With this upgrade, the Arduino board becomes much more flexible as a microcontroller driver can be configured more than a simple USB to serial converter. It also can convert Arduino to a standard keyboard, mouse, MIDI, and mass storage device. So, there are much more ways to use Arduino now.
But this is not over yet. Arduino decided to change the bootloader too with the new Optiboot firmware that brings some improvements as well. The new bootloader occupies 1.5kB less code space leaving it for applications and loads firmware to flash faster.
After removing the FTDI chip, there was no 3.3V source left that was driven from the FT232RL chip directly. So there is an external 3.3V voltage regulator that can source up to 150mA current needed by some shields. FYI older boards can provide only up to 50mA – this is where the FTDI chip is limited.
New Arduino boards are still compatible with all shields, and also code can be ported from older versions. Regular users should not feel any difference, especially with the UNO board. Extreme Mega2560 will bring additional resources that include more memory, more I/O’s, and more peripherals.