In data networking and transmission, 64b/66b is a line code that transforms 64-bit data to 66-bit line code to provide enough state changes to allow reasonable clock recovery and facilitate alignment of the data stream at the receiver. It was defined by the IEEE 802.3 working group as part of the IEEE 802.3ae-2002 amendment which introduced 10 Gbit/s Ethernet. The overhead can be reduced further by doubling the block size to produce 128b/130b encoding, as used by PCIe 3.0, and a very similar variant is the 128b/132b encoding used by USB 3.1.