Coherent Accelerator Processor Interface (CAPI), is a high-speed processor expansion bus standard, initially designed to be layered on top of PCI Express, for directly connecting CPUs to external accelerators like GPUs, ASICs, FPGAs or fast storage. It offers low latency, high speed, direct memory access connectivity between devices of different instruction set architectures. More details and documentation on CAPI can be found on the OpenCAPI Consortium website and IBM Portal for OpenPOWER.