The microprocessor, or CPU, as some people call it, is the brains of our personal computer. I’m getting into this history lesson not because I’m a history buff (though computers do have a wonderfully interesting past), but to go through the development step-by-step to explain how they work.

Well, not everything about how they work, but enough to understand the importance of the latest features and what they do for you. It’s going to take more than one article to dig into the inner secrets of microprocessors. I hope it’s an interesting read for you and helps you recognize computer buzzwords when you’re making your next computer purchase.

1. Where Did CPUs Come From?

When the 1970s dawned, computers were still monster machines hidden in air-conditioned rooms and attended to by technicians in white lab coats. One component of a mainframe computer, as they were known, was the CPU, or Central Processing Unit. This was a steel cabinet bigger than a refrigerator full of circuit boards crowded with transistors.

Computers had only recently been converted from vacuum tubes to transistors and only the very latest machines used primitive integrated circuits where a few transistors were gathered in one package. That means the CPU was a big pile of equipment. The thought that the CPU could be reduced to a chip of silicon the size of your fingernail was the stuff of science fiction.

2. How Does a CPU Work?

In the '40s, mathematicians John Von Neumann, J. Presper Eckert and John Mauchly came up with the concept of the stored instruction digital computer. Before then, computers were programmed by rewiring their circuits to perform a certain calculation over and over. By having a memory and storing a set of instructions that can be performed over and over, as well as logic to vary the path of instruction, execution programmable computers were possible.

The component of the computer that fetches the instructions and data from the memory and carries out the instructions in the form of data manipulation and numerical calculations is called the CPU. It’s central because all the memory and the input/output devices must connect to the CPU, so it’s only natural to keep the cables short to put the CPU in the middle. It does all the instruction execution and number calculations so it’s called the Processing Unit.

The CPU has a program counter that points to the next instruction to be executed. It goes through a cycle where it retrieves, from memory, the instructions in the program counter. It then retrieves the required data from memory, performs the calculation indicated by the instruction and stores the result. The program counter is incremented to point to the next instruction and the cycle starts all over.

3. The First Microprocessor

In 1971 when the heavy iron mainframe computers still ruled, a small Silicon Valley company was contracted to design an integrated circuit for a business calculator for Busicom. Instead of hardwired calculations like other calculator chips of the day, this one was designed as a tiny CPU that could be programmed to perform almost any calculation.

The expensive and time-consuming work of designing a custom wired chip was replaced by the flexible 4004 microprocessor and the instructions stored in a separate ROM (Read Only Memory) chip. A new calculator with entirely new features can be created simply by programming a new ROM chip. The company that started this revolution was Intel Corporation. The concept of a general purpose CPU chip grew up to be the microprocessor that is the heart of your powerful PC.