Why Integrate a Circuit?

An integrated circuit (IC) is a thin slice of silicon (or other material) that has a tiny electric circuit etched on its surface. The IC and the computer have evolved hand-in-hand for over 30 years. Why is the relationship between the two so close? Partly because the computer, unlike many other electronic systems, demands an incredibly large number of components to function. You can build a functional transistor radio from five transistors, but even in the early days of computers, thousands or tens of thousands of switches, relays, electron tubes, or transistors were needed just to make a computer that, today, would be outperformed by a hand-held calculator. ICs offered a way to make more complex circuits that were much smaller than circuits made with individual or “discrete” components, because an IC can have many millions of microscopic individual elements, including transistors, resistors, capacitors, and conductors. Just as importantly, they require much less electricity so they don’t overheat or gulp enormous amounts of energy.

Why do computers require so many components? Because the heart of computers—their logic and memory functions—are made up of thousands or even millions of nearly identical sets of simple circuits, and each of these circuits requires one or more transistors. Computer logic consists of simple “gate” circuits that process information in the form of pulses of electricity representing ones and zeroes. Everything a computer does—displaying information, calculating the path of a computer game’s ammo, sending an email—is controlled by a program that consists of instructions, translated into “binary” numbers: ones and zeroes. Actions such as keystrokes, mouse clicks, etc., are the “input” to the program. The circuits in a computer deal with the program instructions and the input data by adding or subtracting ones and zeroes, changing zeroes to ones, or comparing numbers to determine if they are alike or different. All that happens inside electronic circuits called gates, which are made up of transistors.

If it’s still unclear how combinations of gates turn 0s and 1s into information displayed on a screen, don’t worry. Study computer science in college and you’ll eventually understand. Complex computer operations require many, many tiny logic decisions to perform the simplest functions, and thousands of simple functions have to be performed simultaneously to do something as complicated as play a game or view a movie. Using the most popular type of construction, each logic gate requires up to four transistors. You can imagine how these add up and why it takes millions of transistors to make even one microprocessor chip.