PCI came out in 1992. Today these slots and its data bus technology are used for things not envisioned when it was under development over 12 years ago. PCI has its limitations and the PCI pro slots never became popular. The limitations are coming to the forefront in delivering multimedia content and Gigabit Ethernet. Of course getting higher frame rates at higher resolution and quality for video games also is an issue. PCI has been evolving over time increasing its speed to five times the original, but it has reached its limits of development. Many say that stretching out the AGP to 8x speed might be pushing at its limit too.

First let us look at the current PCI architecture you will find on most motherboards. The CPU/Microprocessor communicates with the first of two data bridges, normally referred to as the Memory Bridge or Northbridge. The Northbridge not only communicates with the CPU; but also communicates to the AGP port, which is where your main graphics card is (usually the only graphics card). It also communicates with your RAM. The fourth thing it communicates with is the second data bridge, known as the Input/Output (I/O) Bridge or Southbridge. The Southbridge also communicates to your plug in slots/cards, drive controllers, and USB, Fireware/1394, parallel. serial, game, keyboard and mouse ports. The theoretical speed limit of the Southbridge communication to I/O including the PCI slots is 133 MB/second. All of the communications in the system are parallel with none of the data having any priority over any other. Blocks of data have to be sent one at a time and cannot be done concurrently. Therefore the data is transferred from one section of the motherboard to the next section based on the order received, not the importance or whether a piece of data arriving by a certain time to its destination is critical.

PCI Express, instead of using a parallel bus architecture, uses serial networking typology with only two wires for each direction. At higher speeds, it allows concurrent transfer of data while having a similar look and the same type of Northbridge/Southbridge architecture as currently in desktops and laptops.

However, in servers the Southbridge is eliminated producing greater data throughput. The PCI slots initially have a 250 MB/second throughput, but the scalable width technology (increasing the number of wire pairs) enables slots and cards to communicate at 32 times that speed in later implementations using longer slots. But the typology can also use network switching type technology, giving data priority and quality of service functions. Hot plug/swap of components is a native part of the architecture.

The PCI Express Graphics Port, replacing the AGP Port, will have a 4GB/second transfer rate in its initial configuration, double that of the current 8x AGP ports. For laptops units there will be a new plug-in card to replace PCMCIA called ExpressCard. It will come in two forms, one that more looks like a PCMCIA card refereed to at the 34 module form factor (34 x 75 x 5 mm) and a more oversized L looking card called the 54 module form factor (54 x 75 x 5 mm). This new architecture is compatible with existing operating systems. Also the new PCI Express slot is capable of being placed alongside current type PCI slots so a choice can be made which type of card can be used in a motherboard just like was done with ISA slots and current PCI slots. The standard PCI Express slots being put in motherboards this spring (1x) will be a lot shorter than the standard PCI slots.

All of this will mean that a lot of issues having to do with multimedia on desktop and laptop computers will have been solved. It also opens wider use of Gigabit Ethernet on local area networks. It also enables the prospects of new motherboard form factors and computer case designs. As the transition from ISA to PCI was an interesting transition with computer buyers having to do more research and planning on their purchases, the move from PCI to PCI Express will do the same. However, as was with the previous transition, the performance and capability increases of computers will be profound. Further information on PCI Express can be found at www.express-lane.org.

Timothy Everingham is CEO of Timothy Everingham Consulting in Azusa, California. He is also Vice Chair of the Los Angeles Chapter of ACM SIGGRAPHand is also on the Management Information Systems Program Advisory Board of California State University, Fullerton. In addition he is the Vice President of the Windows Media Users' Group of Los Angeles. He is also part-time press in the areas of high technology, computers, video, audio, and entertainment/media and has had articles published throughout the United States and Canada plus Australia, England, & Japan. Further information can be found at http://home.earthlink.net/~teveringham

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