AGP

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A Guide for Online Information About: Accelerated Graphics Port (AGP) by Naveen PN The Accelerated Graphics Port (AGP) is an effort to improve the graphics performance of a PC. According to its developer Intel, AGP technology provides a dedicated, high-speed port for the movement of large blocks of 3-D texture data between the PC's graphics controller and system memory. AGP is a new interface specification based on PCI, but was designed especially for the throughput demands of 3-D graphics. AGP introduces a dedicated point-to-point channel so that the graphics controller can directly access main memory. Related Links: Read the Technology Overview of AGP from Intel's site. Data transfer speed and modes of AGP The AGP channel is 32 bits wide and runs at 66 MHz (at 1× mode). This translates into a total bandwidth of 266 Mbps, as opposed to the PCI bandwidth of 133 Mbps. Such a high speed is achieved by transferring data on both the rising and falling clock edges. Also, AGP makes use of sideband transfers and pipelining so it can constantly transfer data without depending on other components in the PC. AGP also supports two optional faster modes, with throughputs of 533 Mbps (2× mode) and 1.07 Gbps (4× mode). In addition, AGP allows 3-D textures to be stored in main memory rather than video memory. AGP uses what is known as Direct Memory Execute ( DiME). Using DiME, the AGP chips have the capability to access main memory directly for the texture mapping and other memory intensive operations. Texture maps can be accessed from system memory in two ways: pipelining—improves performance by letting the sequential parts of tasks overlap sideband addressing—AGP uses eight extra "sideband" address lines, which allow the graphics controller to issue new addresses and requests simultaneously while data continues to move from previous requests on the main 32 data/address wires Additionally, AGP doesn't share bandwidth with other devices, whereas the PCI bus does share bandwidth. Related Links: Read more about the data transfer speeds in different modes of AGP System requirements for AGP The PC chipset must support AGP. The motherboard must have an AGP bus slot or must have an onboard AGP graphics system. The operating system must support AGP. Benefits of AGP Main benefits are: peak Bandwidth four times the PCI bus and higher sustained rates via sideband and pipelining Direct Memory Execute of textures reduced PCI bus hogging Related links: More benefits of AGP -from Intel's web site. Conclusion In the early days of AGP, there was a lot of skepticism regarding its capabilities. Many thought that the AGP was no better than PCI. But, AGP definitely outruns the PCI interface in terms of data transfer speed. Today many PCs come bundled with an AGP as a standard device. Some of the motherboards even integrate AGP chips. AGP is certainly the solution for future graphics workstations and other graphics intensive applications. Links to AGP related sites on the Internet: Intel's AGP site The AGP FAQ—answers common questions about AGP http://sysopt.earthweb.com/agp.html—an article on AGP Tutorial on AGP by Intel—a good tutorial on AGP. Hear it from the horse's mouth! Webopedia's definition of AGP AGP forum website—AGP Implementors Forum AGP Explained—from Anadtech.com An article on AGP at PCMechanic Does AGP Really Improve Performance? by Tomshardware.com Intel's press release about AGP AGP nomenclature Page at agpforum.org AGP specifications Circuit Cellar provides up to date information for engineers, www.circuitcellar.com for more information and additional articles. ©Circuit Cellar, the Magazine for Computer Applications. Posted with permission. For subscription information, call (860) 875-2199 or e-mail subscribe@circuitcellar.com


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