Graphics address remapping table: Difference between revisions

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{{short description|I/O memory management unit for graphics}}

The '''graphics aperture remapping table''' ('''GART''')<ref>[http://support.amd.com/techdocs/25112.pdf Software Optimization Guide for AMD64 Processors]</ref> or '''AGP-GART''' when used with [[Accelerated Graphics Port]], sometimes known as the '''graphics translation table''' ('''GTT''')<ref>{{cite web|author=freedesktop.org|url=http://dri.freedesktop.org/wiki/GART|title=GART|accessdate=2010-03-05}}</ref>, and often misintepreted as '''graphics address remapping table''' is an [[IOMMU|I/O memory management unit]] (IOMMU) allowing the graphics card to perform a [[direct memory access]] (DMA) to the host system memory. Introduced by AMD for mapping of 32-bit AGP [[graphics card]]s accesses to the 64-bit memory space of the [[AMD64]] processors<ref>[https://pdfs.semanticscholar.org/60f1/35af3eb5253394f4ff944062a1b9e6a0c564.pdf Utilizing IOMMUs for Virtualization in Linux and Xen]</ref>, it was later reused for [[PCI Express]] (PCIe) as well.

The '''graphics address remapping table''' ('''GART'''),<ref>{{Cite book|url=http://esd.cs.ucr.edu/webres/agp20.pdf|title=Accelerated Graphics Port Interface Specification: Revision 2.0|date=4 May 1998|pages=24}}</ref> also known as the '''graphics aperture remapping table''',<ref>{{Cite book|url=http://www.playtool.com/pages/agpcompat/agp30.pdf|title=AGP V3.0 Interface Specification|date=September 2002|pages=116}}</ref> or '''graphics translation table''' ('''GTT'''),<ref>{{cite web|author=freedesktop.org|url=http://dri.freedesktop.org/wiki/GART|title=GART|accessdate=2010-03-05}}</ref> is an [[IOMMU|I/O memory management unit]] (IOMMU) used by [[Accelerated Graphics Port]] (AGP) and [[PCI Express]] (PCIe) [[graphics card]]s. The GART allows the graphics card [[direct memory access]] (DMA) to the host system memory, through which buffers of [[texture mapping|textures]], [[polygon mesh]]es and other data are loaded. [[AMD]] later reused the same mechanism for [[I/O virtualization]] with other peripherals including [[disk controller]]s and [[network adapter]]s.<ref>[https://support.amd.com/TechDocs/48882_IOMMU.pdf AMD I/O Virtualization Technology (IOMMU) Specification, 32-bit to 64-bit Legacy I/O Device Mapping]</ref>

A GART is used as a means of data transferexchange between the [[primary storage|main memory]] and [[video memory]] through which buffers (i.e. paging/swapping) of [[texture mapping|textures]], [[polygon mesh]]es and other data are loaded, but can also be used to expand the amount of video memory available for graphicssystems cards,with particularlyonly forintegrated cardsor withshared graphics (i.e. no dedicateddiscrete videoor memoryinbuilt graphics processor), such as [[Intel HD Graphics]] processors. However, this type of memory (expansion) remapping has a caveat that affects the entire system: specifically, any GART, pre-allocated memory becomes pooled and cannot be utilised for any other purposes but graphics memory and display rendering.

==Operating system support==

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|work = docs.sun.com

|publisher = [[Sun Microsystems]]

|archive-url = https://web.archive.org/web/20090323100129/http://docs.sun.com/app/docs/doc/819-2254/agpgart-io-7i

}}</ref>

|archive-date = 2009-03-23

|url-status = dead

}}</ref>

== See also ==

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[[Category:Graphics hardware]]

[[Category:Peripheral Component Interconnect]]