Why Do Most CPUs Only Use Around 1 Volt? Isn't That Really Weak?

When you consider the operating voltage of modern CPUs, it often seems quite low—typically around 1 volt. However, this voltage is not only effective but critical for several reasons. In this article, we will explore why CPUs use such a low voltage and what benefits they bring.

The Power of Low Voltages

One of the primary reasons for using low voltages in CPUs is their remarkable power efficiency. As we know, the power consumed by a CPU is proportional to the square of the voltage, as described by the formula (P V^2/R). A small decrease in voltage can lead to a substantial reduction in power usage. This is crucial for both performance and thermal management in modern computing devices.

Efficient Heat Management

Low voltage operation is also beneficial for heat management. Lower voltages result in less heat generation, which is a major limiting factor in CPU performance. By keeping the temperature within safe operating limits, CPUs can achieve higher performance without requiring extensive cooling solutions. This is particularly important for portable devices like laptops and smartphones where overheating can significantly impact battery life and device performance.

Transistor Design and Efficiency

Modern CPUs utilize advanced transistor technologies such as FinFETs, which are specifically designed to work efficiently at lower voltage levels. These transistors can switch on and off extremely quickly, allowing CPUs to maintain high performance without the need for high voltages. This design has allowed CPU manufacturers to enhance performance while maintaining power efficiency.

Scaling and Performance

As technology has advanced, manufacturers have been able to scale down the size of transistors, enabling them to operate effectively at lower voltages. This scaling, combined with architectural improvements, has helped maintain performance levels while using lower voltage. This trend has been key in making CPUs both more powerful and more energy-efficient.

DVFS: Dynamic Voltage and Frequency Scaling

Modern CPUs also employ dynamic voltage and frequency scaling (DVFS). This technology allows CPUs to adjust their voltage and frequency based on workload. During less demanding tasks, the CPU can lower its voltage even further, saving power without sacrificing performance.

Historical Context and Voltage Reduction

It is worth noting that CPUs like most electronic devices used to operate at much higher voltages, such as 5 volts. As CPUs became faster, the need to reduce power consumption became more critical. Consequently, the voltages were gradually reduced to improve efficiency and performance.

At the most basic level, lower voltages allow for faster swings in the CPU's operation from one state to another. For example, it takes less time to swing a voltage from 1V to 0V and back compared to swinging it from 3.3V to 0V and back. This efficiency translates to higher clock speeds and faster overall performance.

Loren M. Lang wisely pointed out that if a 1V CPU takes 100W, the 5V version would take at least 2500W to achieve the same performance, assuming the square of the voltage difference. This simple power calculation further emphasizes the efficiency gained from using lower voltages.

In summary, while a voltage of 1V may seem low, it is optimal for balancing performance, power efficiency, and thermal management in modern CPUs. Lower voltages are a critical factor in achieving both high performance and efficient power usage in today's computing devices.