MapReduce is a great approach to problem solving. It is very popular too, but MapReduce examples other than word-count are scarce on the web. This article describes MapReduce problem solving that is beyond word-count.
Arduino uses asynchronous serial communication to send-receive data to and from other devices. Arduino Uno supports serial communication via on-board UART port and Tx/Rx pins. Generally this transmission happens at 9600 bits per second which is termed as baud rate.