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PCI Express Basics 101
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Vineel Kovvuri - http://vineelkovvuri.com

Contents
========

    1 - Introduction
    2 - References

1. Introduction
===============

    PCI Express: It is a standard which comes in multiple generations and multiple
    lane configurations. PCI-E is in its 5th generation, but mostly the current
    shipping generation is 3rd generation also called as Gen 3. Mainly each
    generation improves upon the previous generation regarding the speed per lane
    supported by the protocol.

    Below is the table for each generation and lane speed
    For single-lane and 16-lane links, in each direction:

    ========== ========== ==========
    Generation x1         x16
    ========== ========== ==========
    Gen 1      250 MB/s   4 GB/s
    Gen 2      500 MB/s   8 GB/s
    Gen 3      985 MB/s   15.75 GB/s
    Gen 4      1.969 GB/s 31.51 GB/s
    Gen 5      3.938 GB/s 63 GB/s
    ========== ========== ==========

    There are PCIE connectors in x1, x2, x4, x8, x16 configurations. The
    specification also makes sure in an x16 physical connector we can plugin in any
    card with x1, x2, x4, x8, x16. One important fact about physical connectors is,
    x16 physical may not be powering all the 16 lanes so for example in a
    motherboard if an x16 connector is fueling only x4 lanes, it means, The
    connector is limited to x4 speeds.

    
    Different type of physical PCIE connectors

    Now to understand each connectors capability we need to refer the motherboard
    manual. They explicitly talk about the supported connectors and their
    configuration for the CPU maximum supported lane count. After all CPU max
    supported PCI-E lane count is what matters and how the motherboard takes
    advantage of these lanes.

    
    Gigabyte Motherboard manual description of on board PCIE connectors and their
    configurations

2. References
=============

    - How PCI Express Works|https://computer.howstuffworks.com/pci-express.htm