PCI Express (PCIe) - The Universal Mainboard Bus
High-speed serial point-to-point bus for GPUs, NVMe storage, network and capture cards. Slots x1, x4, x8, x16 - generations 1.0 to 6.0 with up to 256 GB/s.
PCI Express (PCIe) is the dominant internal expansion bus on every modern PC and server mainboard. Unlike its predecessor PCI (parallel), PCIe is a serial point-to-point link with one or more lanes, each carrying a differential pair in each direction. Slot widths are denoted by the number of lanes: x1, x4, x8, x16 - and slot lengths grow accordingly.
Higher-numbered slots are backward compatible: an x4 card runs in an x16 slot at full bandwidth; an x16 card runs in an x8 slot at half bandwidth (some boards even allow physical x16 in x4 mode). Generations are also backward compatible: a PCIe 5.0 card works in a PCIe 3.0 slot, throttled to the slower generation.
Generation Comparison
| Version | Year | Bandwidth per lane | x16 total | Encoding |
|---|---|---|---|---|
| PCIe 1.0 | 2003 | 250 MB/s | 4 GB/s | 8b/10b |
| PCIe 2.0 | 2007 | 500 MB/s | 8 GB/s | 8b/10b |
| PCIe 3.0 | 2010 | 985 MB/s | 15.75 GB/s | 128b/130b |
| PCIe 4.0 | 2017 | 1.97 GB/s | 31.5 GB/s | 128b/130b |
| PCIe 5.0 | 2019 | 3.94 GB/s | 63 GB/s | 128b/130b |
| PCIe 6.0 | 2022 | 7.88 GB/s | 126 GB/s | PAM4 + FLIT |
Typical Slot Layout
| Slot | Pins | Length | Typical use |
|---|---|---|---|
| x1 | 36 | 25 mm | Sound cards, USB controllers, NICs |
| x4 | 64 | 39 mm | NVMe SSDs, RAID, capture cards |
| x8 | 98 | 56 mm | 10G/40G NICs, mid-range GPUs |
| x16 | 164 | 89 mm | GPUs, AI accelerators, PCIe risers |
Matching products
- PCIe expansion cards (USB, SATA, NIC, capture)
- PCIe risers and ribbon cables
- M.2 NVMe-to-PCIe adapters
Frequently Asked Questions
Can I run a PCIe 5.0 GPU in a PCIe 4.0 slot?
Yes. PCIe is fully backward compatible - the link will negotiate down to the slower generation. Real-world performance loss for current GPUs at 4.0 vs 5.0 is typically below 5 %.
How is the GPU powered when the slot only delivers 75 W?
The PCIe x16 slot itself supplies up to 75 W. High-end GPUs add 6-pin (75 W), 8-pin (150 W) or the new 12VHPWR connector (up to 600 W) directly from the PSU.
What is M.2 versus PCIe?
M.2 is a small form-factor edge connector that uses PCIe lanes (or SATA, depending on the key) to connect NVMe SSDs and Wi-Fi modules. Electrically it is PCIe; mechanically a different socket.
Related connectors
- ATX 24-pin mainboard power
- S-ATA Power for drives
- Molex 4-pin (legacy)
- USB 3.x
- Internal connector overview
Procurement & engineering support: Phone +49 7666 88499-0 · sales@industry-electronics.com · B2B pricing, volume discounts, custom assemblies on request.