Editing PCI Express (section)

=== PCI Express 1.0a <span class="anchor" id="1.0"></span><span class="anchor" id="1.0a"></span> ===
In 2003, PCI-SIG introduced PCIe 1.0a, with a per-lane data rate of 250&nbsp;MB/s and a [[transfer (computing)|transfer rate]] of 2.5 gigatransfers per second (GT/s).

Transfer rate is expressed in transfers per second instead of bits per second because the number of transfers includes the overhead bits, which do not provide additional throughput;<ref name="HroAC" /> PCIe 1.x uses an [[8b/10b encoding]] scheme, resulting in a 20% (=&nbsp;2/10) overhead on the raw channel bandwidth.<ref name="tfQxK" /> So in the PCIe terminology, transfer rate refers to the encoded bit rate: 2.5&nbsp;GT/s is 2.5&nbsp;Gbit/s on the encoded serial link. This corresponds to 2.0&nbsp;Gbit/s of pre-coded data or 250&nbsp;MB/s, which is referred to as throughput in PCIe.

==== PCI Express 1.1 <span class="anchor" id="1.1"></span> ====
In 2005, PCI-SIG<ref name="n9qGs" /> introduced PCIe 1.1. This updated specification includes clarifications and several improvements, but is fully compatible with PCI Express 1.0a. No changes were made to the data rate.