Peripheral Component Interconnect

Peripheral Component Interconnect
Jonathan Zander · CC BY-SA 3.0 · source
Name	Peripheral Component Interconnect
Introduced	1992
Designer	Intel
Successor	PCI Express
Bus width	32-bit, 64-bit
Clock speed	33 MHz, 66 MHz
Voltage	5 V, 3.3 V

Peripheral Component Interconnect

Peripheral Component Interconnect is a computer bus standard for connecting peripheral devices to a motherboard, introduced by Intel in 1992. It became widely adopted across IBM PC compatible systems, found in servers from Sun Microsystems, workstations by SGI, and desktop platforms from Compaq and Dell. The standard influenced later interfaces used by Apple Inc., HP, Lenovo, and embedded platforms in Siemens and Cisco Systems equipment.

Overview

PCI provided a platform-neutral expansion bus used by hardware makers such as NVIDIA, AMD, Intel, Broadcom, and Realtek to implement network cards, graphics adapters, storage controllers, and sound cards. Major operating systems including Microsoft Windows NT, Linux (kernel), FreeBSD, OpenBSD, and NetBSD implemented drivers and subsystem support for PCI enumeration and configuration. The standard was managed and extended through industry groups and companies like PCI-SIG, with input from corporations such as IBM, Hewlett-Packard, Motorola, and Toshiba.

Architecture and Operation

PCI defines a shared parallel bus architecture with a host bridge connecting to CPU families like Intel Pentium, AMD Athlon, and DEC Alpha. Devices on the PCI bus are identified by bus, device, and function numbers and use configuration space accessed via mechanisms standardized for platforms such as x86, PowerPC, and SPARC. The bus supports memory-mapped I/O and programmed I/O models used by drivers in Microsoft Windows 95, SunOS, and Linux distributions to perform DMA transfers with controllers from vendors like Marvell and Promise Technology.

Technical Specifications

PCI specifications describe widths of 32-bit and 64-bit data paths, clock domains at 33 MHz and 66 MHz, and signaling voltages that evolved from 5 V to 3.3 V variants. Electrical, timing, and protocol details were formalized by PCI-SIG and influenced implementation choices by manufacturers such as VIA Technologies, Intel Corporation, and Texas Instruments. Addressing, interrupt routing, and bus mastering behavior are described alongside connectors and mechanical guidelines that informed designs from ASUS, Gigabyte Technology, and MSI (company).

Expansion Slots and Form Factors

Motherboard slot types and mezzanine form factors supported by PCI include full-length and half-length cards used in systems from Dell, HP, and Lenovo; compactPCI variants used in industrial systems by Advantech and Kontron; and laptop docking implementations adapted by Toshiba Corporation and Sony. Low-profile brackets, riser cards for servers from IBM and Fujitsu, and embedded modules in products by Siemens AG and Beckhoff leveraged PCI mechanical standards. The standard coexisted with other form factors such as AGP, ISA, EISA, and later PCI Express.

Device Types and Drivers

Typical PCI devices included graphics adapters from NVIDIA and ATI Technologies, Ethernet controllers by Intel and Realtek, SCSI and RAID controllers by Adaptec and LSI Logic, and sound cards from Creative Technology. Operating system drivers for these devices were developed by vendors and communities around projects like X.Org, Wine (software), and the Linux kernel driver model. Firmware interfaces such as BIOS and later UEFI performed PCI device enumeration and resource allocation during boot on platforms from ASUS, Gigabyte Technology, and MSI (company).

Performance and Compatibility

PCI provided modest bandwidth appropriate for 1990s-era peripherals; practical throughput depended on bus width, clock rate, and contention among devices. Servers from Sun Microsystems, HP, and IBM used multiple buses and bridge chips to mitigate bottlenecks, while graphics-intensive workstations from SGI and desktops from Compaq and Dell favored higher-speed buses like AGP and later PCI Express. Compatibility was maintained through plug-and-play conventions adopted by Microsoft and open-source projects such as Linux kernel, though physical and electrical incompatibilities required attention when mixing 5 V and 3.3 V cards from vendors like VIA Technologies and Intel Corporation.

Historical Development and Successors

PCI evolved through revisions driven by consortiums including PCI-SIG and contributions from corporations like Intel, IBM, DEC, AMD, and Toshiba. It coexisted with older buses such as ISA and newer interfaces like AGP before being superseded in mainstream systems by PCI Express. Embedded and industrial uses persisted in compactPCI and proprietary blends by companies including Advantech, Kontron, and National Instruments until serial point-to-point interconnects from PCI-SIG and initiatives from Intel and AMD completed the transition. Legacy PCI support remains in virtualization stacks from VMware, QEMU, and KVM for compatibility with operating systems like Microsoft Windows NT and Linux (kernel).

Category:Computer buses