PCI and PCI-Express Slots All There is to Know

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PCI (Peripheral Component Interconnect) and PCI-e (PCI-Express) slots connect peripheral hardware into your motherboard.

It sounds simple now, but dont get too comfy: from conventional PCI, to PCI-e x1, to PCI-e x16 ports, and from connecting GPUs, to sound cards, to network cards, there are many specifications to look out for in these motherboard ports.
This guide will go over exactly what you need to know as a builder, when looking at PCI ports on a motherboard, as well as going over their relevancy, uses, and examples of hardware that would connect into them.
First, well go over conventional PCI slots.

Conventional PCI Slots:

These ports are the grandpas of PCI-Express slots, suffering from carpal tunnel and joint pain.

Standard until 2003, when PCI-e 1.0a was introduced, these older PCI slots are still somewhat relevant today, as these slots still are provided in many motherboards, though the phasing out of this weaker technology is definitely occurring.

As these ports have a sluggish data transfer rate of 133 MB/s, and a 33.33 MHz clock speed, theyre typically home to slower peripherals, such as:

  • fan controllers
  • network adapters
  • ridiculously low-end graphics cards

PCI-Express:

This newer expansion bus was specifically designed to replace PCI ports, and that it does, with each generation of PCI-Express port being marginally faster than the previous, while still all being backwards-compatible with older PCI-e generations.
The first version, PCI-E 1.0a released in 2003, already trampled the conventional PCI port, doubling the per-lane data rate, and having 7.5x the clock speed.

Buying a motherboard today, though, youll more likely find PCI-e 2.0 ports.

These much improved PCI-e slots, released in 2007, are true to the 2.0 title. This newer port doubles the data rate and transfer rate of the PCI-e 1.0 port, and the vast majority of peripherals will not saturate the capabilities of this port. For this reason, this is the PCI-e expansion bus that is widely found on motherboards today.
This being said, PCI-e 3.0 is a thing.

Yet again justifying its title, this 2010 PCI-e 3.0 port runs blazing fast, with bandwidth doubling the previous PCI-e 2.0 ports. For this reason, the first device that was built to be compatible with the 3.0 generation PCI-e slot was the Radeon HD 7970, released in early 2012.

Though all the recently released GPUs nowadays are compatible with PCI-e 3.0, running them in PCI-e 2.0 will not subject it to any noticeable decrease in performance. This being said, PCI-e 3.0 is currently becoming increasingly implemented in motherboards, so its likely that you wont need to compromise.

It doesn’t stop here: there’s also many different sizings for PCI-e slots, explained next.

PCI-Express Form Factors:

For different needs, are different sized PCI-e ports.

Currently, the sizings for PCI-e include include the small x1 slot, the x4 slot, the x8, and the most common, x16.
The naming scheme comes not necessarily from the size, but from the bandwidth speeds: the x4 is four times faster than the x1, and the x8 doubles the possible speeds of the x4.

This being said, the x4 and x8 is plenty fast, and installing a GPU on a x4 or x8 port rather than a standard x16 port will not subject your GPU to any noticeable speed decrease; there is theoretically a performance decrease as there are fewer data channels for the GPU to work with, but the performance difference is negligible, and you will likely not notice any difference.

PCI-e x1 will fit many small peripherals, such as:
  • usb 3.0 expansion cards
  • sound cards
  • low-profile GPUs.
PCI-e x4 is home for the same peripherals, as well as: 
  • Sata card controllers
  • internal Solid State Drives
While PCI-e x8 and x16 are the ports used mainly for GPUS.

As a final note, keep in mind that these ports, more often than not, will be backwards-compatible; a sound card for the x1 slot can usually fit a x4 or above, without causing any trouble. Therefore, PCI-e x16 ports are the optimal ports to look for when buying a motherboard.

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