MoboCop · 10-06-2004 · Category: Tech-planations

PCI Express

The Peripheral Component Interconnect (PCI) is the specification used by the computing industry since 1992 as the local bus system within a computer. The specification standardized how PCI expansion cards, such as a network card or modem, install themselves, and exchange information with the CPU. But over the years, while CPU frequencies have risen from 66 MHz in 1993 to over 3 GHz in 2003 (two orders of magnitude larger), the operational frequency of PCI has only increased once. The result is the current PCI bandwidth hardly begins to feed the I/O processing capability of today's CPUs.

The new Input/Output (I/O) standard, PCI Express, changes all that. Appearing in systems starting in 2004, PCI Express is technically not a new generation of PCI architecture, but an architectural leap. It keeps the core of PCI's software infrastructure, but completely replaces the hardware infrastructure with a radically new forward-looking architecture that rockets I/O back into the express lane of performance.

PCI Express is not only designed to replace the PCI bus for devices such as modem and network cards, but also the Advanced Graphics Port (AGP) used for desktop graphics cards since 1997. Unlike PCI, its parallel predecessor, PCI Express is a serial point-to-point interconnect capable of extremely high-bandwidth transfers. Performance ranges from 250 megabytes per second (MBps) for a single "lane" implementation and up to 4 gigabytes (GBps) for the 16 "lane" implementation likely to dominate the AGP-replacement market. Better yet, there's room to grow and for even faster I/O.

As fast as this is, it doesn't spell the end for PCI. Like the 16-bit ISA (Industry Standard Architecture) bus that PCI replaced, PCI will likely be around for some time, used in implementations that don't require the performance gains of PCI Express. In fact, for the time being, many desktops systems will probably offer PCI expansion slots right alongside one or more PCI Express slots.

Contents

1. Introduction
2. VESA Local Bus
3. PCI
4. AGP
5. PCI Express

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