PCI Express

PCI Express (Peripheral Component Interconnect Express), officially abbreviated as PCIe (or PCI-E, as it is commonly called), is a computer expansion card standard designed to replace the older PCI, PCI-X, and AGP standards. PCIe 2.1 is the latest standard for expansion cards are available on mainstream personal computers.

PCI Express is used in consumer, server, and industrial applications, as a motherboard-level interconnects (to connect the motherboard-mounted peripherals) and as an expansion card interface for the addition of sircuit board. A key difference between PCIe and a bus topology based on previous serial link point-to-point, rather than a shared parallel bus architecture.

PCIe electrical interface is also used in a variety of other standards, especially the ExpressCard laptop expansion card interface.

Conceptually, the PCIe bus can be considered as a substitute for high-speed serial older (parallel) PCI / PCI-X bus. At the software level, PCIe maintaining compatibility with PCI, a PCIe device can be configured and used in legacy applications and operating systems that do not have direct knowledge of the newer PCIe features (but you can not insert a PCIe card into the PCI slot). In terms of the protocol bus, the PCIe communication is encapsulated in packets. Packetizing depacketizing works and traffic-data and status messages are handled by the port PCIe transaction layer (described later). Radical difference electrical signal and bus protocol requires the use of different form factors of mechanical and expansion connectors (and thus, a new motherboard and new adapter board).

Architecture

PCIe, unlike a standard PC expansion earlier, structured around a serial link point-to-point, the pair (one in each direction) to form a pathway, but rather from a parallel bus together. This path is directed by the hub on the main board acts as a crossbar switch. This behavior is a point-to-point dynamic allows more than one pair of devices to communicate with each other at the same time. In contrast, the old PC interface all devices permanently wired on the same bus, so only one device can transmit information at a time. This format also allows channel grouping, in which multiple paths are guaranteed to pair a single device to provide higher bandwidth.

The number of pathways that are negotiated during power-up or explicitly during operation. By making the lane count flexible, a single standard can provide for the needs of high bandwidth card (eg, graphics, 10 Gigabit Ethernet and multiport Gigabit Ethernet cards), while the less economical than a card.

Unlike previous PC expansion interface standards, PCIe is a network of connections point-to-point. This eliminates the need for arbitration bus or waiting for buses that will be free, and allows full duplex communication. While the standard PCI-X (133 MHz 64 bit) and PCIe × 4 has roughly the same data transfer speed, PCIe × 4 will give better performance if the pair multiple devices to communicate simultaneously or if communication between a single device pair is bidirectional.

The format specification is maintained and developed by PCI-SIG (PCI Special Interest Group), a group of more than 900 companies that also maintain the conventional PCI specification.

Interconnect
PCIe devices communicate via a logical connection called an interconnect or link. link is a communication channel point-to-point between the two PCIe ports, which allows both to send / receive regular PCI-demand (configuration read / write, I / O read / write, memory read / write) and cut (INTx, MSI, MSI-X). At the physical level, a link consists of one or more lanes. low-speed peripherals (such as a Wi-Fi 802.11) using a single-lane (× 1) links, while the graphics adapters typically use 16-lane link wider (and thus, faster).

PCI Express (standard)
PCIe card will fit into a slot or larger physical size, but can not get into a smaller PCIe slot. Some of the slots using an open socket to allow the physical card anymore and will negotiate the best available electrical connections. The number of lines actually connected to a slot may also be less than the number of slots supported by the physical size. Example a is a x8 slot that actually only runs at × 1; these slots will allow any card × 1, × 2, × × 4 or 8 to be used, although it only runs at 1 × speed. This type of socket is described as × 8 (× 1 mode) slot, meaning physically receive up to × 8 cards but only runs at 1 × speed. The advantage gained is that many larger PCIe cards can still be used without requiring the motherboard hardware to support full transfer rate, which keeps costs down design and implementation.

PCI Express Mini Card
PCI Express Mini Card (also known as the Mini PCI Express, PCIe Mini, and Mini PCI-E) is a replacement for the Mini PCI form factor based on PCI Express. Express. It was developed by PCI-SIG. The host device supports PCI Express and USB 2.0, and using each card where the designer feels most appropriate to the task. Most laptops are built after 2005 are based on PCI Express and can have several mini card slot.

External PCIe video cards
Theoretically, External PCIe graphics notebook can deliver the power of the desktop by connecting your notebook to desktop video card PCIe (enclosed in its own external housing), but only one finished product and there are two product concepts. All three video cards provide power to external display only, and all connected to the notebook via an ExpressCard interface, which limits the bandwidth of the video card inserted × 16 (4 GB / s in each direction), only × 1 (250 MB / s in each direction )

IBM / Lenovo also includes PCI-Express slots in their Advanced Docking Station 250310U. It provides a half-size slots with x16 slot length, but only x1 connectivity. However, docking station with expansion slots became less common as laptops get more advanced video card and both DVI-D interface, or DVI-D to pass through the port replicators and docking stations.

Additionally, the Quadro Plex Nvidia has developed an external PCIe Video Card that can be used for advanced graphics applications. These cards require PCI Express × 8 or × 16 slots for interconnecting cables. AMD recently announced ATI XGP technology based on proprietary cabling solutions compatible with PCIe transmission signal.