PCI-X 2.0 and PCI Express introduced an extended configuration space, up to 4096 bytes. The only standardized part of extended configuration space is the first four bytes at which are the start of an extended capability list. Extended capabilities are very much like normal capabilities except that they can refer to any byte in the extended configuration space (by using 12 bits instead of eight), have a four-bit version number and a 16-bit capability ID. Extended capability IDs overlap with normal capability IDs, but there is no chance of confusion as they are in separate lists.