A computer has many parts.
Some parts fit into slots. These slots help parts talk. You can add sound or web parts. They help your computer work.
Do you like computers?
A computer has many parts.
Some parts fit into slots. These parts help the computer work. You can add sound or web parts.
These parts use a special path to talk. The path helps them share information. Some parts are small and fit in laptops.
These parts help your computer do more. It is fun to see how they work.
A computer has many parts that need to talk to each other.
One way they do this is through a PCI bus. PCI stands for Peripheral Component Interconnect. It is a set of steps that lets hardware connect to a computer.
You can use it to add a sound card or a network card. You can even add a card for your hard drive.
Some parts are built right onto the main board. Other parts are expansion cards that fit into slots.
To make sure you do not use the wrong power, cards have notches. These notches are small cuts in the metal. They act like keys on a lock. They help the card fit into the right slot.
PCI was very popular from 1995 to 2005. Later, a new way called PCI Express became more common. Most modern computers use PCI Express now. However, some special computers still use the old PCI way. This helps them use older parts that still work well.
A computer needs many ways to connect different parts together.
One important way is through the Peripheral Component Interconnect, or PCI. This is a local bus used to attach hardware devices. A bus is like a path that carries information. PCI is helpful because it uses a standard format. This means it works with many different types of processors.
You can use it to add many useful tools. These include sound cards, network cards, and even modems. Some parts are built directly onto the main motherboard. Other parts come as expansion cards that fit into slots.
Working with PCI involves a very organized way of sharing.
The bus is parallel, which means it moves data in groups. It is also synchronous to a single bus clock. This clock keeps everything moving at the right time. When a device connects, it gets an address. This address lets the processor find it easily. The system uses a special space called Configuration Space to do this. At startup, the computer's firmware checks all the buses. It finds every device and gives it the resources it needs. This includes memory space and interrupt lines.
To keep things fair, the bus uses Latency Timers. These timers make sure one device does not take all the bandwidth.
Intel first developed the very first PCI specification.
Later, a group called the PCI Special Interest Group took over. They became responsible for making the standard better over time. PCI was first used in IBM PC compatible computers. It replaced older, slower ways of connecting parts like ISA and VLB. In servers, it replaced other systems like MCA and EISA. By 1996, the VLB system was almost extinct. Apple also started using PCI for its professional computers in 1995. This helped their Power Macintosh computers work much better.
There are many different versions of PCI to know.
The first version found in desktop computers was a 32-bit bus. It used 5 volts of power for its signals. Version 2.0 added 3.3 V slots to the mix. These slots have a different shape to prevent mistakes. You can tell them apart by looking at the notch. A universal card has two notches so it fits both types.
There is also a faster version called PCI-X for servers. PCI-X 1.0 can reach 133 MHz. Even faster is PCI-X 2.0, which can reach 533 MHz. There is also Mini PCI, which is made for laptop cards.
PCI was the most popular choice from 1995 to 2005.
Since then, a newer way called PCI Express has taken over. PCI Express uses a different, serial architecture. Because of this, many modern motherboards do not have PCI slots. However, you can still find them on some modern desktops. This is done to keep things backward compatible. It also helps because these parts can be cheap to make. Some industrial computers still use these older cards today. Many things that used to need a card are now built-in. You might now find these features in a USB port instead.
Peripheral Component Interconnect, commonly known as PCI, is a local computer bus.
A bus is a communication system that transfers data between components. PCI provides a standardized format for attaching hardware devices to a computer. This standard is independent of any specific processor's native bus. This independence allows different types of hardware to work with various processors. PCI can connect integrated circuits on a motherboard or expansion cards in slots.
These devices might include network cards, sound cards, modems, or even TV tuner cards. Because it provides a common language, PCI became a vital part of computer architecture.
To understand how PCI works, we must look at its organized communication methods. It is a parallel bus, meaning it moves multiple bits of data at once. The bus is synchronous to a single bus clock. This clock ensures all components move in perfect timing. When a device connects, it is assigned an address in the processor's address space. This allows a bus master to treat the device as if it were directly connected.
To manage resources, the system uses a PCI Configuration Space. During startup, firmware or an operating system queries this space. It identifies which devices are present and what resources they need. The system then allocates memory space, I/O port space, and interrupt lines to each device.
Sharing the bus requires strict rules to ensure every part gets a turn. PCI uses Latency Timers to manage this process. These timers help bus-mastering devices share the bus fairly. Fairness means one device cannot use so much bandwidth that others cannot work.
Additionally, devices use interrupt-request lines, or IRQs, to signal they need service. The PCI bus includes four interrupt lines labeled INTA# through INTD#. In many systems, up to eight devices can share a single IRQ line. To prevent one line from becoming too crowded, the positions of these lines rotate between slots. This rotation helps spread the load evenly across the available lines.
There are several distinct types and versions of the PCI standard. The original 32-bit version used 5-volt signaling and a 33.33 MHz clock. This setup could reach a peak transfer rate of 133 megabytes per second. Version 2.0 introduced 3.3 V slots to support different voltages.
These slots use a physical notch to prevent users from inserting the wrong card. Universal cards feature two notches so they can work with both 5 V and 3.3 V. Version 2.1 added an optional 66 MHz operation for more speed. For laptops, a smaller version called Mini PCI was introduced in version 2.2.
There is also CardBus, which is an external connector standard for laptops.
Server-oriented hardware often uses a more powerful variant called PCI Extended, or PCI-X. This version operates at much higher frequencies than standard PCI. PCI-X 1.0 can reach frequencies up to 133 MHz. The newer PCI-X 2.0 can reach speeds up to 533 MHz.
While consumer PCs mostly used 32-bit versions, the 64-bit variant of PCI was used in professional Apple Power Macintosh computers. This 64-bit version provided a much larger memory address space. These specialized versions allow servers to handle much heavier workloads than a standard desktop.
The history of PCI began at the Intel Architecture Labs. Engineers there defined the architecture and created a proof-of-concept platform called Saturn. Intel later partnered with other teams to bring it to market. The first PCI specifications were developed by Intel, but the PCI Special Interest Group (PCI-SIG) later took over development. PCI first appeared in IBM PC compatibles. It was very successful at replacing older, slower systems like ISA and VLB. In the server market, it replaced Micro Channel architecture (MCA) and EISA. By 1996, the VLB system had almost entirely disappeared from the market.
PCI held its peak popularity in the desktop market from 1995 to 2005.
Eventually, the need for more bandwidth led to new technologies. The Accelerated Graphics Port (AGP) was used for video cards before PCI Express arrived. PCI Express uses a serial, lane-based architecture, which is different from the parallel structure of conventional PCI. Because of this change, many modern motherboards have removed PCI slots entirely. However, some modern desktops still include them for backward compatibility. Industrial PCs also continue to use PCI for specialized expansion cards. Many functions once requiring a PCI card are now built directly into motherboards or handled by USB.
Where will your curiosity go next?
🖼️ Images & Media (12)
More to explore
✨ What else?
Related topics you might enjoy
🔬 Go deeper
More advanced topics to explore
🪜 Step back
Simpler topics to build understanding
What is Nepedia?
A free, ad-free encyclopedia for children. Every article is written at five reading levels, so the same page works for a five-year-old and a fifteen-year-old — use the level switcher above to see this one change. No account needed to read.