AGP Bus

Accelerated Graphics Port

[AGP Bus Description]
[AGP Standard] [AGP Interface ICs] [AGP Pinout]
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AGP Bus Description

AGP [Accelerated Graphics Port] is a Point-to-Point [Chip-to-Chip] bus using 1.5 Volt or 3.3V signaling. The main use of the AGP bus is as a Local Video bus in IBM compatible Personal Computers [PCs].
The AGP interface bus is based on the PCI [Peripheral Component Interface] spec, using the PCI specification as an operational baseline. The AGP specification adds 20 additional signals not included in the PCI bus.
The AGP specification defines the Protocol, Electrical and Mechanical aspects of the bus. Refer to this page for a comparison of Video bus through-put for different expansion buses.

The Mechanical definitions include a connector and AGP Board [Add-in card]. The Card sizes and 1.5v and 3.3v connectors are also defined within the spec.
There are five connectors defined: AGP 3.3v, AGP 1.5v, AGP Universal, AGP Pro Universal, AGP Pro 3.3v, and AGP Pro 1.5v. PCI and AGP boards are not mechanically interchangeable.





The AGP 1.0 specification defined 1x and 2x speeds with the 3.3v keyed connector.
The AGP 2.0 specification defined 1x, 2x and 4x speeds with the 3.3v, or 1.5v keyed connector or a 'Universal' connector which supported both card types.
The AGP Pro specification defined 1x, 2x and 4x speeds with the 3.3v, or 1.5v keyed connector or a 'Universal' connector which supported both card types.
The AGP 3.0 specification defined 1x, 2x, 4x and 8x speeds with the 1.5v keyed connector or a 1.5v AGP Universal / Pro connector.
Each up-grade is a supper-set of the 1x mode, so 4x will also support the 1x speed. The base clock rate is 66MHz, but to achieve to 2x, 4x, and 8x speeds the clock is doubled each time. AGP uses both edges of the clock to transfer data.

AGP (1x): 66MHz clock, 8 bytes/clock, Bandwidth: 266MB/s [3.3V or 1.5V signal swing]
AGP 2x: 133MHz clock, 8 bytes/clock, Bandwidth: 533MB/s [3.3V or 1.5V signal swing]
AGP 4x: 266MHz clock, 16 bytes/clock, Bandwidth: 1066MB/s [1.5V signal swing]
AGP 8x: 533MHz clock, 32 bytes/clock, Bandwidth: 2.1GB/s [0.8V signal swing], still uses 1.5 volt motherboard power

The AGP data bus may be 8, 16, 24, 32, or 64 bits. Due to timing requirements the maximum bus length is 9". The trace impedance is specified as 65 ohms +/- 15 ohms (no termination resistor is specified).
For the 8x speed the bus requires a parallel termination or 50 ohms. Some lines may require a Pull-Up Resistor to insure the lines come out of reset in the proper state.
The AGP Interface is optimized for FR4 PCB designs. Both 4 layer and 6 layer PCBs have been studied.

AGP 2.0 pin out, 2 rows of 66 finger [pins]. The Pin Outs for AGP 3.0 specification differ from the AGP 2.0 Standard.
Not all AGP cards will work in all AGP slots. Use the table below, to determine if an AGP board will function in a particular motherboard. The AGP pinout list is provided lower down the page.

AGP Card / Motherboard Functionality
 
AGP 2.0 Cards
AGP 3.0 Cards
MotherBoard 3.3 Connector 1.5 Connector Universal Connector Universal AGP3.0 Connector AGP3.3 Connector
AGP 3.3 Works Keyed Wrong Works Keyed Wrong Keyed Wrong
AGP 1.5 Keyed Wrong Works Works Works No Function
AGP Universal Works Works Works Works No Function
Universal AGP 3.0 Keyed Wrong Works Works Works Works
AGP3.0 Keyed Wrong No Function No Function Works Works

AGP 3.0 boards only work off of a 1.5 volt connectors / Mother Boards
There are three different key configurations for AGP cards: 3.3v keyed [1x, 2x], 1.5v keyed [4x, 8x], 1.5v universal keyed [1x, 2x, 4x].





AGP Standards and Specifications

Accelerated Graphics Port Interface Specification; Revision 1.0 1996
Accelerated Graphics Port Interface Specification; Revision 2.0 1998
Accelerated Graphics Port Interface Specification; Revision 3.0 2002

As of the middle of 2005 many Mother Boards are now shipping with a PCI Express card slot instead of an AGP card slot. Some Mother boards are still offering either bus interface.
Mother Boards using either AMD or Intel processors have moving to the PCIe interface bus, actually the chip-sets are moving to support PCIe.
The standard replacement for the AGP bus is the PCI Express x16 bus, which operates at 4 times the rate of the 8x AGP standard.

Some mother boards provide an integrated graphics core and don't require a video card.
When an AGP slot is supplied, but the video core is on the motherboard, the expansion slot may be used by an AGP Inline Memory Module [AIMM] to increase the video memory by 4MB.

The AGP Specifications may be down-loaded from Motherboards.org


AGP Board Pinout Tables

Refer to the data above to indicate which version of the standard handles which voltage and speed.
AGP Version 1.0 Pinout: AGP Bus Speed is 1x, 2x, at 3.3 volts. AGP Pinout ver 1.
AGP Version 2.0 Pinout: AGP Bus Speed is 1x, 2x, or 4x, at 3.3v or 1.5 volts. AGP Pinout ver 2.
AGP Version 3.0 Pinout: AGP Bus Speed is 8x, at 1.5 volts. AGP Pinout ver 3.


AGP Component Manufacturers

The AGP interface is an out-dated expansion bus as this point.
AGP chipsets and bridges that supported AGP have been produced in the past.
However support should have declined as the market for AGP products has reduced.
The last two companies producing AGP ICs [listed here] were Intel and Silicon Integrated Systems Corp.
There may be second source vendors that still have stock of old parts, but new designs should not be considered.



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Accelerated Graphics Port Card Edge Connector Manufacturers
It's highly doubtful that there are companies producing connectors for the AGP interface.
The AGP expansion bus connector was keyed to only accept the different styles of AGP cards.
That means for a company to produce a connector for AGP, it could only be used for that interface.
So the same condition applies with the connectors that did with the connector, there's no market.
Meritec was the last connector manufacturer listed on this page, carrying Right Angle AGP Connectors.

AGP Expansion Board
AGP Expansion Card

The listing for Accelerated Graphics Board Manufacturers, or OEM AGP Board Manufacturers has been removed.
The AGP board is considered a Daughter card, or expansion card to the MotherBoard.

AGP: Accelerated Graphics Port
IGP: Integrated Graphics Processors
GPU: Graphics Processor Unit
UAGP: Universal Accelerated Graphics Port


AGP Search Trends showing declining interest, covering the years, 2004 to 2011. Google
AGP Search Trends, 2004 to 2011

Interest in the AGP bus continues to decline. The flagged letters just represent news articles regarding the AGP interface.

Although it's not definitive by the amount of people using Google to look-up the phrase AGP, it does indicate declining interest.
That translates to computer uses opting for another graphics card other than the Accelerated Graphics Port.
And it doesn't mater if the expansion card is an AGP Pro, AGP Universal, or regular AGP Slot.
The fact remains that AGP is a Mature PC Graphics Standard, in need of replacement because it's out-dated.
The current state-of-the-art Expansion Board for video graphics is the PCIe interface.
Unfortunately the up-grade path requires a new mother-board to accept the new card format.

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Modified 2/26/12
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