Definition of PCI Express

The common hardware interface in PCs, Macs and other computers for connecting peripheral devices such as storage drives and graphics cards. PCI Express (PCIe) was introduced in 2002 as “Third Generation I/O” (3GIO), and by the mid-2000s, motherboards had at least one PCIe slot for graphics. PCIe superseded PCI and PCI-X.

Switched Architecture – Multiple Lanes

Unlike its PCI predecessor, which used a shared bus, PCI Express is a switched architecture of up to 32 independent, serial lanes (x1-x32) that transfer in parallel. Each lane is full duplex (see illustration below).

Internal and External for Laptops

A mini PCIe came out for laptops (see Mini PCI Express) and Thunderbolt extends PCIe outside the computer (see external GPU). For PCIe/PCI comparisons, see PCI-SIG. See PC data buses, PCI, M.2, ExpressCard, Thunderbolt and PCI-X.

 PCI Express   Data Rate (each direction)
 Version   1 Lane  4 Lanes  16 Lanes
           (MBps)        (GBps)

 Gen 1      250       1        4
 Gen 2      500       2        8
 Gen 3      984       3.94    15.85
 Gen 4     1969       7.88    31.51
 Gen 5     3938      15.75    63.02
 Gen 6**   7877      31.51   126.03 

  ** = planned for 2023

Parallel Transfer of Serial Channels

PCIe on the Motherboard

M.2 Over PCIe

Different Sizes of PCI Express

PCIe Replaced AGP for Graphics