When referring to the Arduino, unless explicitly stating a specific chip, most people are actually referring to the AT328P chip, which is a chip with 8-bit arch

When referring to the Arduino, unless explicitly stating a specific chip, most people are actually referring to the AT328P chip, which is a chip with 8-bit architecture (registers are 8-bit, 16-bit data types are split between a high and a low register). It has 32 KB programmable memory, and 2 KB RAM. Indeed, though, on the Arduino platform, an int is usually 16 bit, but not because that's the chip's native archticture, but because that's the range required. Though I can't say for sure, I highly doubt (and now am actually almost completely certain in my doubts) that it would promote two chars to ints to perform operations on them, and last night also realized why, namely, there are counts for the number of cycles required to do operations on various data types [0]. If what you say about integer promotion is true, there would be no difference in clock cycles between an int and a byte, but there is. So in essence, no, the Arduino is definitely somehow deviating from spec when it comes to promotion. [0]: https://forum.arduino.cc/index.php?topic=92684.msg696420#msg696420 https://forum.arduino.cc/index.php?topic=92684.msg696420#msg... EDIT: I just realized, I think I need to actually look into the (Atmel's) AVR specs, as the Arduino IDE is basically just a wrapper for that.