The Apple S4 is the integrated computer in the Apple Watch Series 4 and is a custom-designed "System in Package" (SiP) by Apple Inc. The S4 introduced 64-bit ARMv8 cores to the Apple Watch. The chip contains two Tempest cores, which are the energy-efficient cores found in the A12. Despite the small size, Tempest still uses a 3-wide decode out-of-order superscalar design, which make them much more powerful than previous in-order cores. The S4 contains a Neural Engine that is able to run Core ML. Third-party apps can use it starting from watchOS 6.