<p><pre><code> Microcontrollers come in 8-bit, 16-bit, 32-bit, and even 64-bit variants.
</code></pre>
4-bit microcontrollers have existed for a couple decades now: they're used for clocks, timers, etc. The Epson MCUs come with a built-in LCD driver: <a href="http://global.epson.com/products/semicon/products/mcu/4bit_index.html" rel="nofollow">http://global.epson.com/products/semicon/products/mcu/4bit_i...</a>