"ARM big.LITTLE is a heterogeneous computing architecture developed by ARM Holdings, coupling (relatively) slower, low-power processor cores with (relatively) more powerful and power-hungry ones. The intention is to create a multi-core processor that can adjust better to dynamic computing needs and use less power than clock scaling alone.
In October 2011, big.LITTLE was announced along with the Cortex-A7, which was designed to be architecturally compatible with the Cortex-A15. In October 2012 ARM announced the Cortex-A53 and Cortex-A57 (ARMv8-A) cores, which are also compatible with each other to allow their use in a big.LITTLE chip. ARM later announced the Cortex-A12 at Computex 2013 followed by the Cortex-A17 in February 2014, both can also be paired in a big.LITTLE configuration with the Cortex-A7."