Accelerated Graphics Port
[AGP
Bus Description]
[AGP
Standard] [AGP Interface
ICs] [AGP Pinout]
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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.
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| 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].
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 be 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 are 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
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 Version 2.0 Pinout: AGP Bus
Speed is 1x, 2x, or 4x, at 3.3v or 1.5 volts.
AGP Version 3.0 Pinout: AGP Bus
Speed is 8x, at 1.5 volts.
Silicon Integrated Systems Corp. {Chipsets, AGP 8X bridge}
ATI Technologies Inc {Chipsets with AGP bus support}
Intel {Chipsets with AGP bus support, 8x interface}
Accelerated Graphics Port Card Edge Connector Manufacturers
Meritec
{Right Angle AGP Connectors; Universal, 3.3v, 1.5 volt}
Accelerated Graphics Board Manufacturers
OEM AGP Board Manufacturers are listed on the COTS Card Manufacturer page.
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
Engineering Design Key words: AGP bus, Accelerated Graphics Port Standard, AGP Pro, AGP Universal, AGP Slot, Expansion Board, Video card, Slot, Interface based on the PCI bus Standard, PC Local video bus Specification, Spec, IBM Compatible Personal Computer Interface, IC, Physical Interface, Description, Visual display devices, Jitter, Architecture, Guidelines, Mature PC Graphics Standard
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