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Author Topic: Say Fudo, whats with ATI's bandwidth choice for the R770?  (Read 4766 times)
DarkElfa
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« on: June 25, 2008, 03:54:54 PM »

Looking at the specs, I don't understand why ATI didn't choose to go with 512 bit GDDR5 memory instead of the 256 as it would have theoretically given them higher bandwidth than the GTX 280 and possible given them a better match up?
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Smills
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« Reply #1 on: June 26, 2008, 04:22:55 PM »

If they had used a 512bit bus it would have increased the production costs significantly and further raised the price of the graphics card. Additionally, due to the massive speed of the GDDR5 memory, it wouldnt have made much difference to its performance anyway.
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reaperrr
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« Reply #2 on: June 28, 2008, 12:13:35 AM »

Also, memory bandwidth has less impact on performance than many people think. Look at the 2900 XT, much more bandwidth than any other card of that generation (even more than 8800Ultra), yet performance is only roughly on par with 9600 GT, 8800GTS 640 and 3870. Even the 3850 can deliver the same performance in some cases, even though it has just half the bandwidth (and lower core clock on top of that).
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fudo
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« Reply #3 on: July 08, 2008, 05:00:36 PM »

RV770XT gets the right balance as 256 bit works great with GDDR5, a match made in heaven
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DarkElfa
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« Reply #4 on: July 09, 2008, 07:14:34 PM »

So you think that with PCIE 2.0, a 512 wouldn't have been faster?
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Eliot
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« Reply #5 on: July 18, 2008, 11:30:46 AM »

So you think that with PCIE 2.0, a 512 wouldn't have been faster?

That depands on the game and how it does use memory. PCIe 2.0 x8 equals PCIe 1.1 x16 in speed, so the more textures you can fit in the local memory the less a game has to load them while gaming. Also it depands how much memory your computer has and if the game is a native 64bit one. While the external memory on the RV770 is still 256bit, internally ATI is still using it's 512bit ringbus system to compensate a 256bit only approach.

With more bandwidth you most of the time can save time while loading new levels, the most stuttering while gaming comes not from the graphics-card itself (except you use a crappy card) but from the OS which starts swapping when the game is using huge amounts of memory to the harddisc and vica versa. The best way to avoid that are 4GB and a native 64bit game which can access more than 2GB for sure (some 64bit games still have the 2GB restriction because the game was not modified to handle more).

More bandwith means you need more layers on the PCB because you need twice as much paths to make it work, the more layers a PCB gets the bigger the chance to screw up and failure of the PCB in the production process.
At a price-point of €129,-/USD 179,- for a HD4850 there is no room for such screw-ups.

best,

Eliot
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fwoot
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« Reply #6 on: July 18, 2008, 02:40:21 PM »

that was hectic Huh
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Eliot
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« Reply #7 on: July 20, 2008, 06:05:56 AM »

that was hectic Huh

hmm Huh

best,

Eliot
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