Specifications

Computer Architecture and Maintenance (G-Scheme-2014)

done by adding eight extra 8-bit buses which allow the graphics controller to issue

new AGP requests and commands at the same time with other AGP data flowing via

the main 32 address/data (AD) lines. This results in improved overall AGP data

throughput.

In addition, to load a texture, a PCI graphics card must copy it from the system's

RAM into the card's Video memory, whereas an AGP card is capable of reading

textures directly from system RAM using the graphics address remapping table, which

reapportions main memory as needed for texture storage, allowing the graphics card to

access them directly. The maximum amount of system memory available to AGP is

defined as the AGP aperture.

Data Transfer rate

• The AGP transfers axe 32 bits wide, but use 66.66 MHz clock speed.

• The AGP lx transferred I bit per data line per clock cycle yielding 266,66

Mbytes/s.

• The AGP 2x and 4x transferred 2 and 4 bits per data line per clock cycle yielding

533.33 and 1,06666 Mbytes/s respectively.

• The latest AGP 8 transfers 8 bits per data line per clock cycle yielding 2133.28

Mbytes/s. This implementation of AGP is

• already available in the latest motherboards and chipsets. AGP 8x is usually used

in graphics intensive applications like video editing, 3-dimensional mapping, etc.

Feature of AGP

 Peak Bandwidth 4x the PCI bus, and higher sustained rates via sideband

and pipelining.

 Direct Memory Execute of textures.

 Reduced Contention with the CPU and 1/0 devices for bus and memory

access. The PCI bus serves disk controllers, LAN chips, and possibly video

capture. AGP operates concurrently with and independent from, most

transactions on PCI. Further, CPU accesses to system RAM can proceed

concurrently with the graphics chip’s AGP RAM reads, because of so-

called out-of-order and queuing hardware support in the chip set, So

inspite of bean- access from the graphics chip, there should be no audio

breakup or other CPU degradation.

 An “extra port” to the graphics chip for memory access, so it can

concurrently read textures from AGP memory while reading/writing Z-

values and pixels from local memory.

 Allowing the CPU to write directly to shared system AGP memory when

it needs to provide graphics data, such as commands or animated textures.

Prepared By – Prof. Manoj.kavedia (9860174297 – 9324258878 ) (www.kavediasir.yolasite.com)