Graphics address remapping table
The graphics address remapping table (GART), also known as the graphics aperture remapping table, or graphics translation table (GTT), is an I/O memory management unit (IOMMU) used by Accelerated Graphics Port (AGP) and PCI Express (PCIe) graphics cards. The GART allows the graphics card direct memory access (DMA) to the host system memory, through which buffers of textures, polygon meshes and other data are loaded. AMD later reused the same mechanism for I/O virtualization with other peripherals including disk controllers and network adapters.
A GART is used as a means of data exchange between the main memory and video memory through which buffers (i.e. paging/swapping) of textures, polygon meshes 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.
Operating system support
Jeff Hartmann served as the primary maintainer of the Linux kernel's agpgart driver, which began as part of Brian Paul's Utah GLX accelerated Mesa 3D driver project. The developers primarily targeted Linux 2.4.x kernels, but made patches available against older 2.2.x kernels. Dave Jones heavily reworked agpgart for the Linux 2.6.x kernels, along with more contributions from Jeff Hartmann.
- Accelerated Graphics Port Interface Specification: Revision 2.0 (PDF). 4 May 1998. p. 24.
- AGP V3.0 Interface Specification (PDF). September 2002. p. 116.
- freedesktop.org. "GART". Retrieved 2010-03-05.
- AMD I/O Virtualization Technology (IOMMU) Specification, 32-bit to 64-bit Legacy I/O Device Mapping
- Jones, Dave (2003-07-24). "Ugly Ducklings: Resurrecting unmaintained code – agpgart adapted for Linux 2.6 kernel" (PDF). Archived from the original (PDF) on 2014-02-03. Retrieved 2014-06-05.
- "agp(4)". FreeBSD Man Pages: FreeBSD Kernel Interfaces Manual. freebsd.org. 2007-11-28. Retrieved 2014-06-10.
- "agpgart_io manpage". docs.sun.com. Sun Microsystems. Archived from the original on 2009-03-23. Retrieved 2007-12-04.