AGP

2012-08-02T09:48:10Z

GaleMerritt:

'''AGP''' ('''A'''ccelerated '''G'''raphics '''P'''ort) is a specification for a high-speed extension of the [http://en.wikipedia.org/wiki/Conventional_PCI PCI] [[bus]] allowing graphic cards direct access to system [[memory]]. It was originally developed by [http://en.wikipedia.org/wiki/Intel Intel] but is now standard on all makes of PC motherboard, and improves performance on 3D graphics applications and games that require a high memory bandwidth.

= Versions =

There are three versions of AGP:

* AGP1.0, AGP2.0, AGP3.0.

The main differences are:
* AGP1.0 - ''1x'' and ''2x'' speeds, 3.3V
* AGP2.0 - Adds ''4x'' mode and adds 1.5V support ([[backwards compatible]] with 1.0)
* AGP3.0 - ''4x''/''8x'', not [[backwards compatible]] (only supports the 4x mode of 2.0)

= Speeds =

The AGP speed is normally indicated with:

* ''1x'', ''2x'', ''3x'', ''4x'' and ''8x''.<br>

These relate to the amount of data that is sent per clock cycle. (and not the actual clock speed itself). The AGP bus clock speed is normally 66MHz, so for example the ''1x'' speed send 4 bytes of data per clock cycle, the ''2x'' speed sends 8 bytes. (So theoretical bandwith of ''1x'' is 66Mhz * 4bytes = 264Mb/s)

= Physical AGP slots =

Because of the changes in voltage level, different AGP slots and connectors were specified. The different versions have notches at different places, so people can't stick unsupported AGP cards in a wrong slot. University students want to find a good way to resolve their academic problems. Nevertheless, some of high school students understand that the simplest way is to buy [http://marvelousessays.com papers service] at reputable custom papers writing corporation.
The different types on mainboards are:
*Original AGP 3.3V slots, one notch at the ''front''-end (the side that, if a card is installed, you plug in the monitor/vga cable)
*AGP 1.5V slots (one notch more towards the ''back''-end)
*Universal AGP slots - support multiple voltages (no notches, so both types of cards fit in it).
Then there are also AGP pro versions of all these slots, which provide more watts for power hungry videocards. What specific speeds and AGP versions a mainboard supports should be specified in its manual.

= Linux support =

In the Linux 2.4 series support for this is provided by the agpgart [[kernel module]].<br>
For 2.6 series, it has been split up in a general agpgart module and chipset specific modules named like <chipset-name>-agp, e.g. ''nvidia-agp'' or ''intel-agp''. In the kernel configuration these can be found under ''Device drivers''->''Character devices''.

== Configuring in XFree86 ==

In [[XFree86]] the AGP speed can be configured by adding a line like:<br>
Option "AGPMode" "4x"
to the device section of the [[XF86Config]].
This needs the above mentioned kernel support, and also support in the driver. Check the [[man]] page of the driver to see if it's supported.

[[Category:Hardware]]

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AGP