The original ATA standard had to be called PATA (for Parallel ATA) after the advent of Serial ATA for sake of differentiation. PATA refers to an interface used for connecting hard disk and optical drives to the system. It used the parallel mode of data transfer, which peaked at 133 Megabytes per second. Due to the proximity of the data carrying wires, interference was a major bottleneck to greater speeds. Each PATA channel can support two devices in a Master / Slave configuration.