It is a high-speed serial connection that operates more like a network than a bus.
The PCI bus is a 32-bit bus and has 32 lines to transmit data. At the beginning of a transaction, the bus is used to specify a 32-bit address. Once the address is specified, many data cycles can go through. The address is not re-transmitted but is auto-incremented at each data cycle.
The PCI bus has some shortcomings, such as a fixed width of 32 bits and the ability to handle only 5 devices at a time. A new protocol called PCI Express (PCle) eliminates many of these shortcomings, provides more bandwidth, and is compatible with existing operating systems.
Parallelism