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post #1181 of (permalink) Old 08-28-2015, 06:39 PM
KyadCK
Hey I get one of these!
 
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Quote:
Originally Posted by Mahigan View Post

Quote:
Originally Posted by KyadCK View Post

Some incorrect math in there.

990FX stock HT clock is 2.6Ghz but can on some motherboards be overclocked to ~3Ghz. They are not stock clocked at 3.2Ghz. They are also 16-bit links in each direction, not 32-bit. 10.4GB/s unidirectional.

PCI-e 2.0 is 500MB/s/lane pre-encode. That's 8GB/s pre-encoded on an x16, and 6.4GB/s post encode (8/10 encode rate). PCI-e 3.0 is 1GB/s per lane and 128/130 encode rate for just under 16GB/s.

The 990FX board with 3.0 adds a PLX chip on top of that. It takes 32 lanes of 2.0 and splits them into either x16 or x8/x8 of 3.0, including the encoding changes. Hance the latency.

Well if anyone did the math incorrectly it would be AMD. I took the 6.4 GT/s 990FX shot from their PR material. Based on Hardware secrets information, I simply did a 6.4*2 for 12.8 GB/s. If the boards do only function at 2600MHz, rather than 3200MHz according to the PR material, then I am not sure why they would have placed this slide in their information. It would therefore appear to be rather dishonest on their part.

They do use 3.2Ghz HT. Just not on 990FX. More of a server thing.

Just correcting some variables in your equations. Had to do all this math before for other reasons, it helps to have correct numbers, and I have quite a bit of experience with the chipset.

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