Guides/Hardware

Is your graphics card running at full PCIe speed? Check with GPU-Z

By Michael Steininger · Updated October 2026

On most motherboards, only the top long slot is wired for the graphics card's full speed. The lower slots often run with fewer lanes, sometimes just four. A card in the wrong slot still works, so nothing tells you that anything is wrong.

Check with GPU-Z#

1. Download GPU-Z from techpowerup.com and start it.
2. On the Graphics Card tab, find Bus Interface. It reads like PCIe x16 4.0 @ x16 4.0.
3. The first part is what your card supports, the part after @ is what it's running at right now.
4. If the second part is lower, click the small ? next to it and start the render test, then look again.

What the values mean#

• Same on both sides under load, for example x16 4.0 @ x16 4.0: all good.
• Fewer lanes under load, for example x16 4.0 @ x4 4.0: the card most likely sits in a lower slot. Move it to the top long slot.
• Some cards use only eight lanes by design, mostly entry-level models. They show x8 … @ x8 …, and that's correct. Compare the two values, don't look for 16.

Other reasons for fewer lanes#

• On some boards, an SSD in a particular M.2 slot shares lanes with the graphics card slot. The manual lists which slots share.
• Dust or a card that isn't fully seated can make the link fall back. Reseat the card with the PC off and unplugged.
• Riser cables (for vertically mounted cards) can force a lower PCIe version.

Questions#