Difference between AGP Bus and PCI Bus

Key Difference: AGP (Accelerated Graphics Port) and PCI (Peripheral Component Interconnect) buses are based on two different technologies of connecting expansion cards to the computer. AGP is not considered to be a bus as it is connected to only one device. However, it can be referred to as an interface. PCI bus and AGP differs on many aspects and AGP is preferred over PCI for rendering of complex graphic information.

AGP and PCI are technologies that are used to connect expansion cards like video and graphics cards to the PC. AGP stands for Accelerated Graphics Port. AGP defines a high speed and point to point channel designed for Video cards and 3D accelerators. It is not considered as a bus as it connects only one device (video card). However, it is based on the design of a PCI bus; the specification of AGP is based on the PCI 2.1 specification. Intel launched the AGP’s first version in July 1996. This bus was designed to increase the transfer rate of the video cards; in the case of PCI bus, the transfer rate was limited to 133 MB/s. This is also shared among the devices connected to the bus, resulting in even lower transfer rate.

This bus provides the channel through which a graphic controller can directly interact with the system memory. It is fitted into the motherboard and can be considered as the actual expansion slot. Motherboard must support the AGP video card for proper functioning.

On the other hand, PCI (Peripheral Component Interconnect) bus was introduced in 1990 as a cross of ISA and VL-bus. It defines a path through which graphic cards can interact with the CPU. This type of bus can send multiple packets of information and that too from various sources. They all make use of a single path simultaneously. After reaching to the CPU, the information has to wait to get time from CPU. The bus is either a 32 or 64 wide with multiplexed address and data lines. The data through this bus can be transferred continuously for large bursts. The mechanism followed for the transfer can be referred to as a burst. It consists of an address phase and one or more data phases. The interface of PCI contains 256-byte configuration memory which is capable of exhibiting plug and play feature.

Comparison between AGP and PCI:

	AGP	PCI bus
Definition	AGP stands for Accelerated Graphics Port. It is a graphic hardware technology that got introduced in 1996. It defines a high speed and point to point channel designed for Video cards and 3D accelerators.	PCI stands for Peripheral Component Interconnect. The PCI bus architecture has been fully standardized by the PCI Special Interest Group. It is a technology that developed on the features of ISA and VL-bus based technologies.
Main purpose	Solely for use with graphics cards	General I/O interface bus
Type	A point to point connection	Bus
Pathway	A dedicated one between the slot and the processor	Sharing the PCI bus
Graphic Operations	Comparatively faster	Comparatively slow
Peripheral Devices	Comparatively faster	Comparatively slow
Quality of 3D graphics	Comparatively high	Comparatively low
Requests	Pipelined	Non pipelined
Address/Data	De-multiplexed	Multiplexed
Priority Queues	High/low	No priority queues
Number of requests Made	Multiple requests for data during a memory access	One request
Bandwidth	Not shared with other devices	Shared with other devices