E-core (Efficiency core)
The small, energy-efficient core type in a heterogeneous chip — optimized for low power consumption and high throughput per silicon area rather than for raw single-thread performance. It handles background tasks and multithreaded load; several E-cores fit in the same area as one large P-core.
Properties: an E-core (Intel's term; ARM calls them LITTLE, Apple Efficiency) is narrower and simpler than a performance core — fewer execution units, less cache, lower clock — which makes it far more efficient in watts and in transistors. It's not made to be fastest on a single thread, but to (1) run light/background tasks frugally, and (2) provide a lot of multithreaded throughput per area (you can pack many E-cores where one big P-core would fit). Intel's Gracemont/Crestmont E-cores gave big wins in multithreaded workloads without blowing the power budget. It relies on a good scheduler (Thread Director) to make sure the right work lands here. The counterpart to the P-core. Related to P-core and heterogeneous cores.