PCI Express lanes , PCI Express lanes ,PCI Express lanes
PC Guides

Understanding the PCI Express Lanes and Their Bandwidth

The Peripheral Component Interconnect Express (PCIe) is the hardware interface known to connect components to your computer. If you don’t exactly know what a PCIe is, you can refer this article we have published earlier: Information on PCI Express. In this article we stick to explaining you about different connection speeds these PCI Express expansion slots offer you. We also cover details about the lanes architecture in the most simplest of ways.

Before understanding what connection speeds the PCIe are capable of, first let us understand the connection architecture and configurations (x1, x2, x4, x8 and x16).

PCI Express lanes , PCI Express lanes

What are PCI Express Lanes?

Basically the PCI Express doesn’t need any software changes or operating system changes from that of the PCI interface. You can understand why it is so after you go through the steps that are coordinated by the PCI Express.

Immediately after the computer is turned ON, the PCIe quickly identifies what devices are connected to the motherboard and creates a mapping of all the links. It also takes care about the width each device requires for functioning at capable speeds.  

All the above mentioned process which the PCIe undertakes is same as that of the PCI or PCI-X. Hence no software changes are required in the PCIe cards. And can carry out operations in a operating system independent strategy.

So PCI Express lanes are simply wired connections, completely and their functionality is completely hardware related. Each lane consists of two pairs of wires within it. One pair is to send and the other to receive data in the form of bits. These bits move in the form of packets across the lane. The number of lanes present depends on the type of configuration (the number of physical slots).

A x1 connection means that there are four wires involved within one lane. Each bit in the lane moves at the rate of one bit per cycle, into or away from the component attached.

A x2 connection contains 8 different wires in two lanes and can transmit two bits at once. This makes the x2 PCI Express slot twice as fast as the x1 slot. Similarly a x8 can transmit 8 bits at once and an x16 can transmit 16 bits in one cycle. So here you can see there is whatsoever no sharing of the data path at any stage and hence the PCIe is said to employ a serial connection interface. Now that you understood what difference the lanes bring to the PCIe, we can slide into the details of connection speeds.

PCI Express lanes , PCI Express lanes ,PCI Express lanes

What connection speeds are the PCI Express Cards capable of?

A PCI bus can manage speeds up to a maximum of 133 MB every second. Likewise a PCI-X bus with its different configurations could notch up transfer rates of 512 MB to 1 GB per second. The stats shown below will help you realize the difference in speeds the PCI Express brings to you (thanks to the highly optimized serial connection interface)

x1 connection:                        250 MB per second in each direction

x2  connection:                       500 MB per second in each direction

x4 connection:                        Up to 1000 MB per second

x8 connection:                        2 GB per second

x16 connection:                      More than 5 GB per second

All such high speeds can be achieved only using the PCI Express. Also note that these transfer speeds make the PCI Express replace all the earlier connection interfaces.  

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