Graphics address remapping table: Difference between revisions

Revision as of 20:25, 21 August 2019

Revision as of 11:01, 22 August 2019

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

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> oralso 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> sometimes alsoor '''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>

GART is used as a means of data exchange 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 systems with only integrated or shared graphics (i.e. no discrete or inbuilt 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.