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.