The term central processing unit or CPU was developed a long time ago as a term used to identify the portion of the machine that did the actual processing. This term was coined long before the presence of microprocessors and integrated circuits. As technology developed from one form to another, the CPU started to shrink in size. Older CPUs consisted of large vacuum tubes wired together that took up huge spaces, then the appearance of discrete transistors reduced the size of the CPU.
The CPU was further miniaturized with the advent of integrated circuits and microprocessor. The once extremely large and cumbersome CPU was reduced to a very minute piece of silicon with all the connections etched into it already.
A microprocessor is a very advanced integrated circuit that houses millions of transistor within a single package. Along with the transistors within is the circuitry that allows the microprocessor to function and requires little else. The microprocessor was so advanced that it immediately wiped out any other forms of computing. It has managed to contain the CPU, at first in a couple of microprocessors, then finally into a single microprocessor. It has managed to include a few components along the way like a little bit of memory that we now call as the cache.
It is then understandable why the microprocessor and CPU have become interchangeable. The technology of the microprocessor has become so advanced that it has the ability to contain not just one but up to four CPUs inside it, as in the case of quad core microprocessors. And that is not even the limit of what a microprocessor can do.
To put it in perspective, given today’s technology. All CPUs are microprocessors, but not all microprocessors are CPUs. The use of the microprocessor has become so widespread that in a single computer system, there now a number of microprocessors working and they have all but replaced the transistors that were once the king of computer components. The GPU (Graphics Processing Unit) is also contained in a microprocessor. Even the northbridge and southbridge of the computer are both in microprocessors.
To sum up this whole article, the CPU is the brain of a whole computer system. This is where the entire decision making process happens. All the other parts of the computer just obey the requests of the CPU. The microprocessor is an advancement in transistor technologies that allow multiple transistors to be placed in a certain package. It is so advanced and economical that it has become advantageous for manufacturers to utilize the microprocessor in almost every part of the computer.