Apparently, in spite of last week’s suggestions Intel did not add AGP support into its i915-series (Grantsdale) chipsets, but some makers of mainboards had found a way to implement AGP via typical PCI bus, AnandTech web-site reported.
Last week a number of mainboards based on the i915P core-logic with PEG x16 and AGP slots for graphics cards were spotted at Computex Taipei 2004 trade-show. Since Intel’s upcoming chipset was not originally set to support AGP slot, it was a big surprise for hardware community that a number of platform producers implemented the slot that will be phased-out later this year on their new mainboards. However, it appears that AGP on the i915P and SiS656-based mainboards is not native, but is incorporated using typical PCI slots.
Mainboard makers use two PCI slots from ICH6 to “emulate” the presence of AGP. Since two PCI slots only provide 133MB/s bandwidth, performance when using AGP graphics cards drops tremendously. Typical AGP 8x pump up to 2.1GB/s and also sports numerous speed-boosting technologies, such as sideband addressing.
Manufacturers of mainboards believe that additional flexibility with AGP and PCI Express graphics cards is an advantage for consumers, which is doubtful. The majority of end-users acquiring PCI Express-enabled platforms would prefer modern graphics cards and would not sacrifice performance of their PCs. Customers who are not looking for the latest technology are likely to get a previous generation platform that costs much less compared to the cutting-edge flavour of technology.
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Discussion started: 06/08/04 07:46:56 AM
Latest comment: 06/09/04 11:05:59 AM
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> Mainboard makers use two PCI slots from ICH6 to “emulate” the presence of
> AGP. Since two PCI slots only provide 266MB/s bandwidth, performance when
> using AGP graphics cards drops tremendously.
Please learn how PC architecture works.
The PCI bus is a bus. The bandwidth is shared between the slots. You can't "combine PCI slots" to get more bandwidth. The Intel southbridge only supports a single PCI bus.
All this does is remap standard PCI signals into the AGP slot format, and it runs the AGP graphics card in PCI mode, sharing the 133MB/s bandwidth with anything else on the PCI bus. The reason that performance drop is so little is because modern graphics cards have so much memory that they don't need to do many external accesses.
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Posted by: Graham
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Date: 06/08/04 07:46:56 AM]
+ expand thread (4 answers)
- collapse thread
So it's basically a PCI slot in AGP form, then?
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Posted by: Yuri
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Date: 06/08/04 12:58:59 PM]
Yep.
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Posted by: Graham
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Date: 06/08/04 07:19:26 PM]
So what you are saying is that 3DFX was right and NVIDIA wrong. So much about nothing, and who lives was the “wrong” company. Everybody was fooled by marketing.
Who "invented" AGP 4X, 8X anyway? Only needed for the integrated chipset market I guess.
Besides 3DFX, AMD was also one of that said when their 751 "don't" do AGP 2X, that AGP 1X was enough! I'm starting to think when we hear some companies saying you don't need this, just because they don't have it, doesn’t mean they are laying to us (Ati about SM3.0 for example).
The performance of AGP comes from the ability of doing 64bit so the combination of two PCI is possible to deliver better performance. VOODOO2 SLI was an example of this. Voodoo2 SLI on only one board/card is AGP not PCI.
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Posted by: I
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Date: 06/09/04 02:20:58 AM]
AGP is 32bit.
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Posted by: Graham
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Date: 06/09/04 11:05:59 AM]
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