Why is a Microprocessor Commonly Known as a CPU?

The central processing unit (CPU) is at the heart of every modern computer, whether it be a smartphone, a notebook, or a powerful server. Before the advent of microprocessors, CPUs were much larger, often occupying entire cabinets within a complex system of computers and peripherals. This article explores the evolution of the CPU from bulky mainframe computers to the microprocessors of today.

From Mainframes to Microprocessors

Before the microprocessor, CPUs were large and often housed in cabinets along with memory, I/O (input/output) circuits, and various other components. In large data centers, these cabinets would fill an entire room, with each cabinet performing a specific function. The term 'mainframe' refers to the cabinet or large box that houses the processor, along with all its supporting hardware.

Let's look at a restored '1401 processor main frame.' The massive cabinet above is the processor unit, complete with numerous circuit cards that control its operations. Back in the day, entire rooms were filled with these mainframe computers, equipped with tape drives, card readers, and a myriad of other peripherals, all requiring extensive wiring and cooling systems. The room's raised floor was a must to accommodate all the necessary connections and to facilitate easier maintenance.

As technology advanced, minicomputers emerged, shrinking the size of the computing hardware. The CDC 160A, one of the earliest minicomputers, could fit its processor into a desk-sized enclosure. This design allowed the computer to take up considerably less space, sometimes just a portion of a wall. Image (not shown): Dennis Ritchie and Ken Thompson working at a PDP-11, presumably on something UNIX-related.

The Evolution of Integrated Circuits

The miniaturization of CPUs was largely due to the development of integrated circuits (ICs). As ICs gained higher degrees of integration, the number of components that could be packed onto a single chip increased exponentially. This allowed for the creation of CPUs that could fit in a small space, leading to the term 'microprocessor.'

As integration levels improved, the size of individual CPU chips decreased, reaching the point where they could fit on a single piece of silicon, effectively making them micro. Microprocessor chips in modern devices like smartphones and PCs are so small compared to their mainframe predecessors that they can comfortably be held in the palm of a hand. This is in stark contrast to the large processors used in early mainframe computers, which required entire rooms and substantial equipment cabinets.

Understanding the Modern Processor

Frequently, discussions about CPUs can be confusing, particularly when users refer to the entire computer case as the 'processor.' It is essential to clarify that the processor is just one small part inside a much larger system. Just as a car has an engine, a computer has a processor, but the whole computer is not the processor. In the case of mainframe computers, the processor did indeed have a box dedicated to it, much like a train engine has its own train car.

Today, the term 'microprocessor' is used to describe these small, powerful components that perform all the necessary computations in our devices. The prefix 'micro' emphasizes the contrast between the tiny size of modern CPUs and the massive mainframe processors of the past. As technology continues to advance, the size and efficiency of microprocessors will only continue to improve, further impacting our daily lives.