PCI Express – The Shift from PCI Starts Here
If there ever was a shift in PC architecture that was more quick and dramatic than the transition to PCI Express will be, I wasn’t old enough or even alive to remember it. PCI Express, as a technology, will be replacing all the connections on your motherboard including the AGP slot and PCI slots. This transition is being pushed most dramatically by Intel with their new chipset release, though the AMD line won’t be far behind.
PCI Express is a serial bus, much like the new standard in hard drives, Serial ATA. PCIe is also a dedicated bus system, not a shared bus as the PCI and IDE ATA buses currently are. Besides being dedicated, PCI Express also offers up to four times as much bandwidth to the device as the PCI/AGP bus can. Current AGP 8x standards have a bus that supports 2 GB/s of bandwidth on a shared bus that handles both the reads and the writes. However, PCIe with 16 lanes (x16) has separate, dedicated read and write channels for a total of 8 GB/s of bandwidth available to the device.
There have been a lot of arguments against the need for PCI Express in the media recently, and though I would like to tell you they are wrong — I simply can’t. The need for additional bandwidth on the graphics front, over the AGP 8x standard, is simply non-existent for nearly all applications, with the exception being something like editing 4 HDTV streams at one time, which is hardly something a high-end PC gamer or enthusiast would do now.
That being said, PCI Express is important for the future of PCs as it opens the door for larger capacities and faster transfers. Consider PCIe to be as future-proof as you can find a new technology in a current computer.
Moving away from the graphics side of things, there is the topic of the PCI Express as a system bus, replacing the PCI bus on your PC. Using only a single channel (PCIe x1), it can offer up to 500 MB/s which is a dramatic increase over the 75 MB/s that the current PCI bus provides. And to top it off, PCI Express has dramatically lower latency times due to its serial nature. Coupling these things together, you know that higher bandwidth and lower latencies are always going to be a good thing. Of course, we cant’ say that for DDR2, but we’ll get to that in a bit.
Physically, PCI Express is just like any other slot you’ve ever dealt with on a motherboard.
This is an image of a PCIe x16 slot, used for graphics cards, above a standard 32-bit 33 MHz PCI slot. The retention clip is still a necessary device as the video cards are so much heavier than nearly everything else. It is physically a little bit shorter on the PCB than PCI, but you slide the card in just as you would any other AGP card.
This is a standard x1 PCIe slot below a standard PCI slot. It is very reminiscent of a riser slot you have seen on motherboards before. Getting Gigabit Ethernet cards that are only a few inches long will make you do a double take for at least a little while.
Finally, here is a look at the PCIe and AGP connectors. The PCI Express is on top and you can tell that there are dramatically more physical connections on the PCIe card which are somewhat smaller in width.
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