AmbigÃ¼edad

Technology

This standard of local bus was launched by Intel in 1997 to free itself from the bus NCV which it considered too slow for posting in 3D because it ensured only one speed of 132 Mo/s and saw, moreover, its band-width reduced by the number of peripherals that it was to control.

The AGP 32 bits connects the graphic controller to the controller of memory and by offering a speed of 500 Mo/s, with a clock with 66 MHz, but information is transfer on the two faces. Moreover, bus AGP also gives access to the main memory, via the controller of memory, which makes it possible to use this one to store additional data graphic, such as textures or coordinates, thus it became useless to acquire additional video memory to profit fully from the functions 3D of a video circuit.

Alternatives

The port AGP is declined in several alternatives with upward compatibility and whose frequencies are multiples of the basic AGP:

; AGP 1x: bus 32-bit with 66 MHz allowing a rate of maximum transfer of 266 Mo/s, obtained by doubling the frequency of 33 MHz of bus NCV; tension of indication of 3.3 V. ; AGP 2x: bus 32-bit with 66 MHz GDR allowing a rate of maximum transfer of 533 Mo/s; even tension of indication of 3.3 V that the AGP 1x. ; AGP 4x: bus 32-bit with 66 MHz QDR allowing a rate of maximum transfer of 1066 Mo/s (1 Go/s); tension of indication to 1.5 V; ; AGP 8x: bus 32-bit with 66 MHz at eightfold frequency allowing a rate of theoretical maximum transfer of 2133 Mo/s (2 Go/s); tension of indication of 0.8 V.

Nevertheless, in practice, these speeds are not confirmed, because of the DMA, often limited to 100. Moreover, there exist compatibility issues between the various generations, the graphics cards consuming energy more and more. The charts AGP 4x and more do not function any more on the ports AGP 1x , moreover, a locating pin was placed on these charts.

However these interfaces only are partially exploited, because it is especially the speed of the graphic memory which proves to be insufficient. Thus the “top-of-the-range” graphics cards often use memories of technology higher than the main Memory. For example, the “top-of-the-range” graphics cards of ATI were equipped with Mémoire GDDR3 with a BUS of 256 bits.

Food

The professional charts 3D have a version AGP Pro with reinforced food.

AGP 1.0 : 3.3 V - 1x, 2x
AGP 2.0: 1.5 V - 1x, 2x, 4x
AGP 2.0 universal: 1.5 V, 3.3 V - 1x, 2x, 4x
AGP 3.0 (most recent): 1.5 V - 4x, 8x

Standardization

At its exit, Intel created an open group of industrialists whose objective was to ensure the promotion of the specification of bus AGP. Among them ATI, Cirrus Logic, IBM, Microsoft, S3 and Trident.

The graphic map productions could use free the specifications of the bus in exchange of the free use of their work on this subject. This policy had already been used successfully for the buses NCV and USB.

Future

There will be no AGP 16x. The successor of the AGP is the PCI Express which supports as well graphics cards as other charts.

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