Definition: transistor toggle

The act of a transistor changing its state from on to off or off to on. Also called a "transistor state change," the number of transistor toggles that take place within a computer, tablet or smartphone every second is staggering. With state-of-the-art devices, the number is in the trillions and quadrillions per second when the CPU and GPU are running at maximum such as when playing a movie and especially when rendering the graphics in a 3D video game.

Instructions Times Transistors
The toggle computation is the number of instructions executing per second times the number of transistors required to implement each instruction. State-of-the-art smartphones can execute trillions of instructions per second, and each instruction can cause several thousand transistors to change their state.

Even at idle, millions of changes can take place. The least expensive microcontroller chip that sells for less than a dollar can have millions of transistor toggles each and every second. See transistor and microcontroller.

An Orchestration of Perfection
Along with these staggering amounts of changes taking place, each and every toggle must be precise. If a 0 should really be a 1 or vice versa, the whole operation may come to a halt. Now imagine those quadrillions and quintillions of changes occurring every second with absolute perfection, every second of the minute, every minute of the hour, all day long!

If a transistor fails, it may cause the application to abort or not. It all depends on the circuit the transistor resides in because chips may have built-in redundancy in certain areas, typically in memory banks. Sometimes a failing transistor goes undetected because it is not in a critical area of the chip.

An Unpublished Metric
Transistor toggles are not provided to the public, but they are a factor in chip design, and semiconductor designers are very interested in these metrics. The more transistors switching at the same time, the more heat is generated, and that is always a consideration when designing a new chip.

Toggles per Second

When one considers that trillions and quadrillions of transistor toggles can occur every second within an area no larger than a postage stamp, it seems outrageous. In fact, the postage stamp is a whole lot thicker than the combined layers of transistors and interconnections. See active area and space/time.