Arduino vs Raspberry Pi

Microcontroller

Single Board Computer (SBC)

Suitable for interfacing a fair number of sensors and actuators such as motors, LEDs etc., and to control them with precise (milli/microsecond) timing.

Possible to interface sensors and actuators, though not as good as Arduino in this. Precise timing is harder to achieve.

Processes 8 bits at a time at @16 MHz.

Processes 32/64 bits at a time @ 700 MHz - 1.5 GHz (depending on model).

Not suitable for intensive data processing, only basic networking (and that too with additional hardware).

Suitable for somewhat intensive data processing such as audio / videos / images, network-intensive applications (has built-in network hardware).

Operates at 5V, fairly robust and doesn’t get spoilt that easily.

Operates at 3.3V (though it needs a 5V supply), not tolerant of 5V signals on pins and spoils easily if not careful.

Typically does not run an operating system; only one program at a time.

Runs a full Linux OS; can be used like a normal computer.