Efficiency-cores, also known as E-cores, are specifically designed to be power-efficient and handle lightweight, background tasks. Their efficiency stems from few key aspects: 1. **Lower Operating Frequencies:** E-cores usually operate at lower clock speeds compared to performance cores (P-cores). This means they consume less power per instruction, thus increasing battery longevity. 2. **Simplified Micro-architecture:** E-cores have smaller and simpler micro-architecture. They have fewer transistors, which results in less power consumption and less heat generation. 3. **Task Appropriateness:** E-cores are designed to handle frequent, less performance-intensive background tasks efficiently, like syncing emails, notifications, etc. Offloading these tasks prevents high-performance cores from waking up needlessly, saving a considerable amount of power. 4. **Dynamic Load Balancing:** Modern systems with efficiency cores use technologies like big.LITTLE and DynamIQ by ARM or Hybrid Technology by Intel, that dynamically allocate tasks depending on the performance need, which optimizes for power and performance. Therefore, the term "efficient" in context of these cores is in relation to their power consumption and ability to handle simple tasks without the need of the more power-hungry performance cores, resulting in overall power savings.

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.