An Accelerated Graphics Port (AGP) is a point to point channel that is used for high-speed video output. This port is used to connect graphic cards to a computer’s motherboard. It increases the speed at which machines can render graphics while using the system’s resources more efficiently. The primary purpose of an AGP is to convey 3-D images much more smoothly than is possible on a regular PC.
The AGP was developed by Intel in the year 1996 and was launched in Socket 7 Intel P5 Pentium and Slot 1 P6 Pentium II processors. Gradually everyone started using it. Chipsets like VIA Apollo VP3, SiS 5591/5592, and the ALI Aladdin V were the first Socket 7 chipsets to support AGP.
Early AGP boards used graphics processors built around Peripheral Component Interconnect (PCI) and were simply bridged to AGP. It can be said that the AGP is built from the PCI that PCI is the base. Bridging didn’t help the cards benefit much from the new bus except for the increased 66 MHz bus clock and the doubled bandwidth over PCI. Intel’s i740 was explicitly designed to exploit the new features of AGP. In fact, it was designed to texture only from AGP memory.
AGP Version Comparison Table
The various versions of AGP are discussed here
|Interface||Clock Speed||Speed||Transfer Rate|
|AGP 1.0||66 MHz||1x and 2x||266 MB/s and 533 MB/s|
|AGP 2.0||66 MHz||4x||1, 066 MB/s|
|AGP 3.0||66 MHz||8x||2, 133 MB/s|
Characteristics of AGP
- It has high quality and very fast performance.
- It has a direct path to the PC’s main memory.
- It connects to the CPU and operates at the speed of the processor bus.
- It sends video information more quickly to the card for processing.
- It uses the main memory to hold 3D images.
- It provides the graphics card with two methods of directly accessing texture maps in system memory: pipelining and sideband addressing.
- The port is identified by its brown colour.
Applications of AGP
- It enabled to develop new classes of applications on the PC such as 3D CAD/CAM, data visualization and 3D user interfaces.
- Direct Memory Execution of textures-The texture maps are directly accessed from the system memory instead of pre-loading the texture data into the Graphic card’s own memory and then accessing it. It eliminates the extra work by allowing the texture to remain in system memory where it can be directly executed on by the graphics chip.
- Creation of 3D images- The CPU must perform intensive 3D calculations. The graphics controller processes the texture data and bitmaps. In many cases, the controller has to read elements from 7 or 8 different textures and combine them into a single pixel on the screen. When this calculation is performed, the pixel must be stored in the memory buffer. The memory occupied by these textures are so large, they cannot be stored on the video card’s buffer. With APG they are stored in the main system memory.
Advantages of AGP over PCI
AGP was introduced as a replacement for the slower Peripheral Component Interconnect (PCI) interfaces. AGP provides a direct line of communication to the CPU and RAM, which in turn allows for quicker rendering of graphics.
Differences between AGP and PCI
|AGP is a port||PCI is a bus|
|AGP normally has a clock speed of 66 MHz||PCI bus normally has a clock speed of 33 MHz|
|AGP normally has a transfer rate of 2, 133 MB/s||PCI normally has a transfer rate of 132 MB/s|
|AGP has a non local memory and is able to access the system memory directly.||PCI has a local memory and relies solely on the memory of the video card.|
|AGP memory allows AGP cards to store texture maps in system memory itself.||PCI stores the texture maps in the memory of the video card itself.|
|AGP receives information simultaneously which makes the graphics quicker and smoother.||PCI receives information in “groups” instead of all at once.|
|AGP makes pipelined or multiple requests for data during a bus or memory access||PCI doesn’t make pipelined request that is it does not make another until the data that is currently requested has been transferred.|