There was an upgrade to the specifications named PCI-X which enabled the PCI to run at 133 MHz.
An advantage of the PCI bus is that devices connected to it can run at one speed while the CPU runs at a different speed.
These cards have now replaced the older ISA (Industry Standard Architecture) cards which used 8 and 16-bit data paths.
These chip-covered PCI cards referred to as adapter cards, expansion cards, add-in cards and plug-in boards plug into the motherboard and do everything the motherboard doesn't.
They provide different services such as allowing you to view information on your monitor, listen to audio and connect to the Internet.
Sometimes your PC's motherboard might have insufficient expansion ports (slots) that are not fast enough and adding expansion cards will greatly enhance your system.
All in all, these ports (slots) share a data 'super highway' referred to as the bus which is a direct electrical pathway to the PC's CPU and main memory. The bus enables fast and direct access to your PC's main resources such as RAM (Memory).
PCI Express is the new standard for computer expansion cards that was introduced to replace the PCI, PCI-X and AGP.
This move from the old parallel bus architecture to the serial bus architecture provided a faster interface for the expansion cards.
The increase in performance was caused by the point-to-point configuration of the serial bus when compared to the shared parallel bus configuration.
All in all, the PCIe bus is really a high speed serial replacement of the older parallel PCI and PCI-X buses.
PCIe technology is under constant development and improvement.
PCI Express 1.0a - This technology started in 2003 and had a data rate of 250 MB/s and a transfer rate of 2.5 GT/s.
PCI Express 2.0 - In 2007, this version doubles the throughput of the PCI Express 1.0 from 250 MB/s to 500 MB/s. This version has a clock speed of 5.0 GHz as compared to version 1.0a at 2.5 GHz. Fotrunately, PCIe 2.0 motherboards slots are fully backward compatible with PCIe version 1.0 cards.
PCI Express 2.1 - This version added just a few improvements to the previous version.
A proposed PCI Express 3.0 is in the pipeline for introduction in 2011. This standard is now in use. This promises a bit rate of 8 GT/s and it will be backward compatible with the existing PCIe standards.
PCI Express replaced AGP as the new interface for graphics cards on present systems.
Since 2009, most graphics cards use PCI Express. nVidia introduced a high bandwidth data transfer technology named Scalable Link Interface (SLI) which enabled multiple video cards with the same chipset and model number to be run in tandem for increased performance.
On the other hand, ATI (now owned by AMD) introduced its version of multiple video cards in tandem called Crossfire.
The two major video card makers nVidia and AMD have released motherboard chipsets that support up to 4 PCIe X16 slots that allows tri-GPU and quad-GPU card configuration.