The different types of processing units used in the chip systems can vary quite a bit, and is often based on the use and the complexity of the device. With a microcontroller, you are generally going to be working with a system that has a very small amount of RAM, and they will generally have just a single chip that controls a limited function. However, some microcontrollers are going to have more peripherals on a single chip. The chip system could also use a microprocessor, which is more common when dealing with systems that are a bit more complex. In some cases, if there is more than a single processor core, you will find that the SOC is actually called a multiprocessor SOC.