PCI Express Guide (2nd Edition)
 

While PCI was a savior when it was released, it too has run out of headroom. With faster hard drives, PCI-based sound cards, etc., the PCI bus was beginning to act like a downtown during rush hour! A new standard was needed to open up additional bandwidth. PCI-Express was the outcome of that development effort to advance the I/O (input output) functionality of today's computers.

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