Efficiency-cores, also known as "little cores" in ARM's big.LITTLE architecture, are designed to be more power-efficient, meaning they consume less energy to perform tasks. This is achieved through multiple means: 1. Lower Clock Speeds: Efficiency-cores typically run at lower clock speeds compared to performance cores, which are geared towards maximum processing power. Since power consumption is proportional to the square of the frequency, operating at a lower frequency greatly reduces power consumption. 2. Simpler Design: Efficiency-cores are generally simpler and smaller in design compared to performance-cores, reducing the amount of energy required to perform a computation. 3. Optimized for Common Tasks: These cores are optimized to efficiently carry out the most common, less-demanding tasks, such as background syncing, email, browsing etc. This combination of performance and efficiency allows for better battery life without sacrificing usability. Devices can switch between performance cores and efficiency cores depending on the computational task at hand. For intensive tasks like gaming or video editing, a device might use more power-hungry performance cores. But for simpler tasks, the device will rely on the efficiency cores, thereby saving power.