IOMMU

In computing, an input/output memory management unit (IOMMU) is a memory management unit (MMU) that connects a DMA-capable I/O bus to the main memory. Like a traditional MMU, which translates CPU-visible virtual addresses to physical addresses, the IOMMU takes care of mapping device-visible virtual addresses (also called device addresses or I/O addresses in this context) to physical addresses. Some units also provide memory protection from misbehaving devices.

An example IOMMU is the graphics address remapping table (GART) used by AGP and PCI Express graphics cards.

AMD has published a specification for IOMMU technology in the HyperTransport architecture. Intel has published a specification for IOMMU technology as Virtualization Technology for Directed I/O, abbreviated VT-d. Information about the Sun IOMMU has been published in the Device Virtual Memory Access (DVMA) section of the Solaris Developer Connection. The IBM Translation Control Entry (TCE) has been described in a document entitled Logical Partition Security in the IBM eServer pSeries 690. The PCI-SIG has relevant work under the terms I/O Virtualization (IOV) and Address Translation Services (ATS).

I/O virtualization is not performed by the CPU, but instead by the chipset.