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PCI vs. PCIe: 4 Differences and Full Comparison

Hi there! If you‘re interested in building, upgrading or customizing a computer, you‘ve likely come across the terms PCI and PCIe. These acronyms refer to two important computer expansion bus technologies that have been integral to major advances in computing over the past 30 years.

In this guide, I‘ll explain exactly what PCI and PCIe are, outline their key differences, and provide a full comparison so you can understand these industry-standard interfaces. Whether you‘re a fellow tech enthusiast or just looking to boost your own PC‘s capabilities, read on to learn everything you need to know about PCI vs PCIe!

What is PCI?

PCI stands for Peripheral Component Interconnect. It is a parallel computer expansion bus standard developed by Intel in the early 1990s to provide a high-speed connection between a computer‘s motherboard and peripheral devices.

Here‘s a quick rundown of key facts about PCI:

  • Released in 1990 by Intel to standardize connections between motherboard and peripherals
  • Used in almost all desktop computers throughout the 1990s and 2000s
  • A parallel interface that transfers multiple bits of data simultaneously
  • Available as integrated motherboard circuits or expansion cards that insert into PCI slots
  • Allows "plug-and-play" connections for devices like graphics cards, TV tuners, WiFi cards, etc.
  • Caps out at speeds of 133 Mbps with a 32-bit, 33MHz architecture

During the 1990s and early 2000s, PCI became ubiquitous in desktop computers, providing an industry-standard way to easily add capabilities through compatible expansion cards. Major iterations included:

  • 1994: PCI 2.0 gains adoption in 2nd-gen Pentium PCs
  • 1995: Apple begins incorporating PCI slots in Power Macs and Performas
  • 1996-2000: PCI improved with new features like 66MHz speed in version 2.2

This widely-used parallel bus gave a major boost to computer graphics, storage, networking and more before eventually being superseded by the newer PCI Express standard.

Brief Timeline of PCI

1990 Intel launches PCI 1.0 after 5 years of development
1994 PCI slots become common on consumer desktops like Pentium PCs
1995-96 PCI adopted by major OEMs including Apple
1996-2000 Incremental PCI improvements released
2004 PCI Express launched as PCI replacement

So in summary, PCI allowed for major performance improvements in 1990s/2000s era computers thanks to its standardized and speedy parallel bus architecture for connecting peripherals and expansion cards. Now let‘s look at how its successor improved upon the original PCI standard.

What is PCIe?

PCI Express (PCIe) is the updated, serialized version of PCI that began replacing it in 2004. Also developed by Intel, PCIe was designed to meet the higher bandwidth needs of modern computing components and architectures.

Some key facts about PCI Express:

  • Launched in 2004 as a sequential evolution of PCI
  • Provides point-to-point serial connections rather than PCI‘s parallel bus
  • Offers much higher maximum speeds, starting at 2.5 Gbit/s for PCIe 1.0 in 2003
  • Has expanded speed dramatically with each version, up to 64 Gbit/s for PCIe 6.0 in 2021
  • Backward compatible with original PCI, but runs older cards at lower speed
  • Available in wide variety of modern form factors and slot configurations
  • Ubiquitous standard for connecting peripherals like GPUs, SSDs, WiFi cards in modern PCs

So in essence, PCI Express retains compatibility with PCI while massively boosting performance through increased bandwidth, higher transfer rates, and serialized communication.

Some key milestones in the ongoing development of ever-faster PCIe versions include:

  • 2003: PCIe 1.0 debuts with 2.5 Gbit/s speeds
  • 2007: PCIe 2.0 arrives, doubling bandwidth to 5 Gbit/s
  • 2010: PCIe 3.0 quadruples speed again to 16 Gbit/s
  • 2017: PCIe 4.0 pushes bandwidth to 32 Gbit/s
  • 2019: PCIe 5.0 doubles throughput again to 64 Gbit/s
  • 2021: PCIe 6.0 hits 128 Gbit/s speeds

Thanks to relentless innovation by Intel and other contributors, PCI Express has continually evolved to provide the improved performance needed for major advances like 4K gaming, GPU acceleration and blazing fast NVMe SSDs.

PCIe History and Generations

Version Year Released Max Transfer Rate
PCIe 1.0 2003 2.5 Gbit/s
PCIe 2.0 2007 5 Gbit/s
PCIe 3.0 2010 16 Gbit/s
PCIe 4.0 2017 32 Gbit/s
PCIe 5.0 2019 64 Gbit/s
PCIe 6.0 2021 128 Gbit/s

Now that we‘ve covered the basics of what PCI and PCIe are, let‘s look at some key differences between these two computer expansion bus technologies.

4 Key Differences Between PCI and PCIe

There are several important distinctions that set PCI and PCI Express apart from one another. Here are 4 of the major differences:

1. Parallel vs. Serial Architecture

One fundamental difference is that PCI uses a parallel bus configuration, while PCIe transmits data serially.

In PCI‘s parallel approach, data is sent simultaneously across multiple physical "lanes" or channels, which enhances throughput. PCIeinstead transmits data sequentially over fewer lanes, simplifying the architecture but requiring increased speed to match or exceed PCI‘s bandwidth.

2. Slot Types and Sizes

The PCI standard only included one type of physical slot that accepted cards of a single set width. PCIe comes in a broad range of slot sizes, shapes and configurations to suit different devices.

For example, small PCIe slots like M.2 are used for SSDs, while large PCIe x16 slots are need for full-sized GPUs. The PCIe interface is much more flexible.

3. Speed and Bandwidth

PCI maxes out at 133 Mbps throughput, while even the original PCIe 1.0 standard operated at 2.5 Gbit/s. Each new generation has exponentially increased PCIe‘s bandwidth well beyond what PCI can offer.

PCIe 6.0 hits a whopping 128 Gbit/s, over 900 times faster than maximum PCI speeds. This massive performance advantage is PCIe‘s most impactful improvement.

4. Error Handling and Reporting

Finally, PCIe also improved upon PCI by baking more robust error detection and reporting into the basic specification. This improves reliability and helps identify issues faster.

PCIe devices continuously monitor for errors and automatically notify systems of any problems. This facilitates diagnostics and repair when something goes wrong.

Comparing PCI and PCIe Specifications

This table summarizes some key specs that differ between the PCI and PCIe standards:

PCI PCIe
Release Year 1990 2004
Bus Architecture Parallel Serial
Slot Type Single standardized slot Many length/sized slots
Max Speed 133 Mbps 128 Gbit/s (PCIe 6.0)
Error Handling Limited Robust built-in features

Now that you understand the core differences under the hood, let‘s explore how these technical contrasts impact real-world performance and use cases.

How PCI and PCIe Compare In Practice

Beyond their underlying specifications, PCI and PCI Express behave quite differently when connecting peripherals or adding capabilities to a PC. Some key practical differences include:

Speed and Performance

PCIe‘s serialized design and massive throughput allows it to support the most demanding modern tech like high-res gaming GPUs, VR headsets, 5G WiFi adapters and bleeding edge SSDs.

PCI‘s parallel bus capped out at 133Mbps, nowhere near fast enough for today‘s bandwidth-hungry devices. The speed difference is game-changing.

Form Factor Flexibility

With PCI you were limited to fixed-sized expansion cards. The range of PCIe connections like M.2 and PCIe 4x/8x/16x enable specialized shapes and configurations tailored to everything from slim SSDs to dual-GPU video cards.

Backward Compatibility

A PCIe slot can accept an older PCI card and run it at legacy speeds. However, a PCI slot can‘t interface with newer PCIe devices. This provides some flexibility in reusing older expansion cards.

Availability and Use

PCIe is standard across desktops, laptops and high-performance servers, while PCI slots have disappeared from modern computers. All new peripherals and expansions rely on PCIe connectivity.

In summary, PCI laid the groundwork for consumer expansion slots, while PCIe built on its legacy to deliver the speed, flexibility and robustness needed for modern computing innovation.

6 Fun Facts Comparing PCI and PCIe

Beyond the technical nitty-gritty, there are some interesting fun facts and stats that reveal how PCIe superseded PCI over time:

  • PCI ruled from 1990-2005 before PCIe overtook it in 2006
  • Intel‘s Architecture Labs (IAL) created PCI as part of the Pentium chipset
  • Apple was among the first major OEMs to adopt PCI in the mid-90s
  • PCIe 1.0 offered 20X the bandwidth of original PCI
  • There have been 6 generations of PCIe so far, each doubling speed
  • PCIe 6.0 hits speeds of 128 Gbit/s, nearly 1000X faster than PCI

So in just over a decade, PCIe expanded from a 20X improvement into an interface that is almost 1000X faster than beloved PCI technology it replaced. That‘s the power of computing innovation compounding over generations!

The Bottom Line

PCI and PCI Express provide the essential interfaces that allow desktop computers, laptops and servers to easily add capabilities through compatible expansion cards and peripherals.

PCI got the party started in the 90s, providing a standardized way to accelerate graphics, storage, networking and more. PCIe built on this foundation but increased speeds exponentially while adding form factor flexibility and robustness.

So if you‘re working on a PC and come across these buzzwords, remember:

  • PCI ruled computing in the 90s and early 2000s
  • PCIe took over in the mid-2000s and still powers modern computers
  • PCIe is much faster, flexible and robust thanks to its serialized design
  • All cutting edge peripherals now rely on some form of PCIe connectivity

I hope this comparison helped demystify these fundamental computer bus interfaces. Let me know if you have any other questions!