What Are PCI and PCI Express and What Is a PCIe Slot

PCI Overview

Developed by Intel Corporation, the Peripheral Component Interconnect (PCI) standard is an industry-standard, high-speed bus found in nearly all desktop computers. So, what is PCI used for? PCI slots let you install a wide variety of expansion cards, including:

• Graphics or video cards
• Sound cards
• Network cards
• SCSI cards
• Many other types of expansion cards

PCI also automatically configures cards to work properly alongside other PCI cards in a computer.

PCI cards are available in both 32-bit and 64-bit versions, and in both 33 MHz and 66 MHz speeds. Running at 32 bits and 33 MHz, a PCI card yields a throughput rate of 133 MBps.

What Is PCI Express (PCIe)?

PCI Express (PCIe) stands for Peripheral Component Interconnect Express and is a high-speed interface used to connect expansion devices to a computer motherboard. PCIe slots are available in different lane configurations and can support devices including graphics cards, network adapters, storage devices, and other expansion cards.

PCI Express, or PCIe is the next evolution of PCI. A PCIe port, or PCIe slot, uses existing PCI programming concepts and communication standards but improves performance to match the speed of modern computers, doubling the data transfer rates of the original PCI bus.

PCIe is different from conventional PCI because it uses a high-speed serial, point-to-point architecture rather than the older shared-bus architecture.

Note: Do not confuse PCI Express with PCI-X (PCI Extended). While similar to PCI Express in function, PCI-X is based on different underlying technology.

PCIe supports the same types of expansion cards as PCI and was designed to be backward compatible with standard PCI cards, so any existing PCI cards can continue to be used. However, a standard PCI card installed in a PCIe slot still runs at the regular PCI speed rather than at PCIe speeds.

What Are PCIe Slots Used For?

PCIe expansion slots are used to add or upgrade hardware components on a motherboard, including:

• Graphics cards
• Network adapters (Wi-Fi and Ethernet)
• Storage devices, such as PCIe/NVMe SSDs
• Sound cards and capture cards
• Other expansion cards requiring high-speed data transfer

PCIe slots come in different physical sizes and lane configurations (such as x1, x4, x8, and x16), which determine how much bandwidth is available to the connected card. A larger slot generally supports more lanes and higher throughput, which is why graphics cards typically use the x16 slot.

PCI vs. PCIe: What is the Difference? 

The core difference between PCI and PCI Express comes down to architecture:

• PCI uses a shared-bus architecture, where multiple devices share the same communication pathway and take turns sending data.
• PCI Express uses a high-speed, serial, point-to-point architecture, giving each connected device its own dedicated communication lane back to the system.

This point-to-point design is what allows PCIe to scale to much higher speeds than conventional PCI while reducing bottlenecks between devices.

PCI Express Errors and Troubleshooting Steps

PCI Express errors fall into two classifications: correctable and uncorrectable errors. The classification depends on whether the error caused a performance issue or affected the functionality of the PCI Express interface.

• Correctable errors are handled automatically by hardware and do not impact functionality, such as data loss.
• Uncorrectable errors:
• Nonfatal: Does not impact the integrity of the PCI Express interface, but data or information is lost. Handled by device-specific software.
• Fatal: Makes the PCI Express interface unreliable, impacting functionality and causing loss of data or information. Recovery requires resetting the component and interface.

If a PCIe device is not detected, or you receive an uncorrectable PCI Express error, run the SupportAssist application. SupportAssist runs a quick diagnostic (and can run a more comprehensive diagnostic) and can also update drivers and optimize your computer.

For more information, see the Dell Knowledge Base article Dell SupportAssist for PCs and Tablets: Frequently Asked Questions (FAQ).

Related resources:

• Dell Knowledge Base article What Are PCIe SSDs and How to Use Them As a Boot Drive for a Dell Computer
• Dell Knowledge Base article Dell Knowledge Base article How to Update Graphics Drivers on a Dell Computer

Frequently Asked Questions

What is PCI Express? PCI Express (PCIe) is a high-speed interface standard used to connect expansion cards, such as graphics cards, network adapters, and storage devices, to a computer's motherboard. It is the modern successor to conventional PCI.

What is the difference between PCI and PCIe? PCI uses a shared-bus architecture where devices take turns communicating over the same pathway. PCI Express uses a high-speed, serial, point-to-point architecture that gives each device its own dedicated lane, resulting in significantly faster data transfer.

Can a PCI card work in a PCIe slot? PCIe was designed to be backward compatible with standard PCI cards in supporting the same card types, but a physical PCI card is not interchangeable with a PCIe slot the way a PCIe card is. Where compatible PCI hardware is used, it operates at standard PCI speeds rather than PCIe speeds.

How many PCIe slots does a computer have? The number of PCIe slots varies by motherboard and computer model. Desktops typically have multiple PCIe slots in different lane configurations (such as x1, x4, x8, and x16), while laptops and small-form-factor systems may have limited or no user-accessible PCIe slots. Check your system's documentation or Dell's Manuals & Documentation page for your specific model's configuration.

What should I do if a PCIe device is not detected? Reseat the card to confirm it is fully seated in the slot, check that any required power connectors are attached, and confirm the slot and card are compatible. If the device still is not detected, run Dell SupportAssist to diagnose the issue and update drivers.