PCI-SIG, the organization in charge of maintaining and developing PCI-Express, has announced that the third version of the PCIe standard is finished and ready for implementation. The new standard is fully compatible with earlier PCIe cards; a Gen 1 or Gen 2 card will run perfectly in a PCIe 3.0 slot.
Just as PCIe Gen 2 offered double the performance of Gen 1, Gen 3 again offers twice the performance of Gen 2 (8GT/s). Unlike Gen 2, however, Gen 3 incorporates a number of additional changes to improve its efficiency. PCIe 1.1 and 2.0 both use an 8b/10b encoding scheme. This means that 8-bit words are mapped to 10-bit packets. This is part of why PCIe bandwidth numbers are quoted differently. Technically, an x1 PCIe Gen 2 slot is capable of transferring 500MB/s, but 20 percent of this is overhead. The actual data transfer peak is 400MB/s. Instead of using the previous 8b/10b scheme, PCIe Gen 3 switches to 128b/130b encoding. This reduces the amount of overhead bandwidth from 20 percent to less than two percent.
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