What is IOMMU (VT-d and AMD-Vi), and why does it matter for DMA?

IOMMU is a part of your CPU and motherboard that controls which memory each device in your PC is allowed to reach. Intel calls it VT-d, and AMD calls it AMD-Vi or just IOMMU. It matters for DMA because a DMA card works by reading memory, and IOMMU is the thing that can say no.

What IOMMU does

Normally, a PCIe device can read and write memory directly. That's what makes graphics cards and fast drives fast. IOMMU sits in between. It gives each device its own map of the memory it may use, and blocks the rest.

• Without IOMMU on, a device can reach any memory it asks for.
• With IOMMU on, a device only reaches what the system has given it.

Windows builds a security feature on top of this called Kernel DMA Protection. Microsoft made it to stop people plugging a device into a Thunderbolt or USB4 port and reading memory while you're away. It needs IOMMU (VT-d on Intel) turned on in your BIOS.

Why games care about it

A DMA card reads the game's memory. If IOMMU is on and the card isn't allowed that memory, it can't read it. So some anti-cheats ask for IOMMU to be on before a game starts.

• VALORANT.
  Vanguard can ask for IOMMU, TPM 2.0, Secure Boot and Memory Integrity before you play. In late 2025, Riot said it enforces IOMMU on accounts it links to DMA devices. It also said some boards reported IOMMU as on when it hadn't been set up early enough in boot, and that board makers shipped BIOS updates for it. In practice, VALORANT nearly always needs IOMMU on. VALORANT DMA.
• Fortnite tournaments.
  Epic asks for Secure Boot, TPM and IOMMU for tournaments. Fortnite DMA.
• Other games.
  More games are adding checks like these. Secure Boot, TPM and IOMMU goes through each setting.

Which of our builds work with IOMMU on

If your game asks for IOMMU, pick a build made for that game. Which DMA firmware should you buy? and DMA on AMD help you choose.

How to check if IOMMU is on

Open System Information (msinfo32) on your main PC and look for Kernel DMA Protection. If it says On, IOMMU is on too. In your BIOS, look for VT-d on Intel boards or IOMMU on AMD boards, often under the CPU or advanced settings. How to check yours has more.

Common questions

• Should I turn IOMMU off?
  Only change it if your build or your game needs it changed. If your game asks for it on, it has to stay on. Ask in a ticket if you're not sure.
• Is VT-d the same as VT-x?
  No. VT-x is for running virtual machines. VT-d is the IOMMU part. Microsoft says Kernel DMA Protection needs both turned on.
• Does IOMMU slow down my PC?
  Not in a way you'd notice in games.
• Can a game damage my card with IOMMU?
  Riot said Vanguard doesn't damage hardware, and that a card blocked by IOMMU can cause errors or instability, which is how IOMMU is meant to work.

Not sure what your game needs? Which anti-cheat does my game use? or ask on the support forum.