How PCIE Works

For many decades, every computer has come from the manufacturer’s lot with expansion slots known as Peripheral Component Interconnect (PCI) slots. These have become such a primary component of every computer’s architecture that everyone just takes for granted now. Nevertheless, the peripherals that have used PCI slots to connect to the computer motherboard have in the years advanced so much in terms of performance, power, and speed that the PCI will soon become redundant. Computer motherboards, processors, sound cards, graphics cards, video cards, and networks have become so advanced while the PCI generally remains the same. The typical PCI can only handle up to 5 devices at any one time and has a fixed 32-bit width with data flowing only in one direction at a time.

There have been attempts to upgrade the PCI and the PCI-X bus is one such attempt that offers higher bandwidth though it complicates some of the PCI’s limitations. The new protocol that has significantly improved performance and efficiently eliminated most of the PCI’s shortcomings is the PCI Express (PCI-E or PCIe). The PCIe provides higher bandwidth and has excellent compatibility with current PCI configurations and operating systems. The PCIe does not only enhance the computer system’s speed, it also dramatically improves graphics performance and potentially replaces the AGP slot.

Video Source: DactaDork

PCIe Connection

The PCI transfers data packets through parallel connections that send multiple data pieces simultaneously. However, these types of connections have their limitations and challenges such as those caused by electromagnetism. The PCIe utilizes highly-integrated serial connections which provide faster data transfers not as a bus but as a network. This works by use of switches that enables the point-to-point connectors to handle data from multiple sources. This has the big advantage that the serial connection divides, labels, and reassembles the data packets for quick transfer. This means each device gets its own dedicated connection and there is no sharing of bandwidth like in the PCI and PCI-X or other normal buses.

PCIE Lanes

Every time you switch on your computer, the PCI-E immediately acts to identify the devices connected to the motherboard. The computer will identify all links such as those from peripheral devices, through the PCIE riser/PCIE Extension Cable, and to the motherboard thus creating a map of how data will flow to and from each device. The PCIe does this through the very same protocols that the PCI does the same so there is no need for changes in operating system or other software. The PCI-E lanes each contain two wires where one sends data while the other receives. Data packets will move across these wires at a rate of a single bit per cycle. Thus, an X1 PCIe connection which is the smallest contains 4 wires which form one lane. The lane will transfer one bit per cycle simultaneously in each direction. The X2 connection transfers two data bits per cycle at once while a X4 carries 4 bits per cycle and so on and so forth.

PCIe Speeds

To best illustrate how superior PCIe is, let us compare it with the other connection types. For instance, a PCI bus 32-bit transfers data at a delivery speed of up to 33MHz. This enables the transfer of up to 133MBps through the bus. Similarly, a PCI-X 64-bit connection will transfer data at twice the speed of the 32-bit PCI. PCI-X connections with the best specifications send about 1GB of data per second. On the other hand, a PCIe lane will handle about 200MBps of data traffic in each direction simultaneously. That means it will transmit a cumulative 400MB of data per second. Thus, a PCIe X1 connection can easily accommodate a gigabit Ethernet connection with storage and audio applications included.

But how does an X16 PCIe connection send as much as 6.4 GB per second in both directions simultaneously? This is done by data prioritization which is a system whereby the PCIE transmits the most important or urgent data first thus avoiding data bottlenecks. Secondly, PCIe relays data in real time in a time-dependent system. Thirdly, the PCIe is so superior in its efficiency due to the technological improvements and the superior materials used. Fourthly, the PCIe utilizes better methods of breaking down data into smaller, more manageable pieces and reassembling the data packets once again. The fact that signals emanating from different data sources have dedicated point-to-point connections and do not have to share resources also increases speed of data transmission substantially.

Conclusion

While PCI connections are still very much in use, the demands by advanced computer users and new technologies are increasing the demand for PCIE connections. For best results, it is better to use a reliable PCIE riser/PCIE Extension Cable to connect peripheral devices to the PCIe slots and the computer motherboard.

The evolution of expansion slots has seen the PCI giving birth to the PCI-X which doubles its speeds and the PCIe which provides an even better data transfer rate over a network rather than a bus. PCIe connections are preferred by data miners, gamers, and other high demand, high-performance users of advanced computer systems.

Todays guest post has been written by Ravinder Balasubramanian is an IT professional