[Kevin] attached a MicroSD breakout board to an Arduino-compatible clone. When the clone starts up, it searches the SD card for a file called ‘program.hex.’ This file is sent over to the ...

A Arduino on a SD carrier already exists – or, at least, an Arduino on a Micro SD carrier. The OpenLog device (Sparkfun). An Arduino, with source code for the data logging function, ...

But it's possible to go even smaller, as the makers of a new Arduino-compatible product called "Microduino" show. At 1" × 1.1", it's nearly as small as a quarter.