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Can each processor core access RAM at full bus speed?

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  • CPUs
  • Core
  • Processors
  • Memory
Last response: in CPUs
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December 23, 2009 11:02:48 AM

Hi,

I'm looking at the Intel Core i5-750 processor and noticed the FSB is rated at 2.5 GT/s.

Can each core transfer data on the bus at that rate? If not, what would be the max speed each core could obtain individually or how would I look that information up. I'm guessing it's in Intel's datasheets somewhere but I'm not sure exactly what to look for.

If I were to buy DDR3 1600 (PC3 12800) memory to use with it, would each processor be able to access the memory at full speed? The maximum memory speed is usually listed on the motherboards but I haven't seen it on the processors themselves yet (on vendor sites). Why is that?

Finally, what tools would you suggest for benchmarking the memory transfer rates, speed, throughput, etc?

Thanks!

More about : processor core access ram full bus speed

December 23, 2009 9:17:11 PM

An Fsb on a Core i5? Shadow of a doubt.

Each core... They share a common L3 on the i5, don't they? So I don't expect them to access the Ram directly.

What you may check in the datasheet is the individual L2-to-L3 throughput. I expect much more than the Ram throughput.

Don't look for Cpu-to-Ram data at the mainboard manufacturer because this data now depends on the Cpu and the Ram, no more on a chipset chosen by the mainboard manufacturer.

You can benchmark with Everest, with the advantage of quick and simple results, which can be compared with many web users. Everest also tells you the Ram settings, very nice to double-check you obtained what you wanted... Other programmes exist, some are better, most are more complicated.
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December 24, 2009 12:55:51 AM


Core i5/i7 can access memory directly with their integrated memory controller. And there is nothing called FSB in Core i5/i7 processors, they are called QPI (Quick Path Interconnect), like HyperTransport in AMD.

And regarding memory speed Core i5 supports Dual channel memory with speed@1333MHz. You can read the article as reference:

http://www.hardocp.com/article/2009/09/07/intel_lynnfie...

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December 24, 2009 6:13:45 PM

Thanks all. Wikipedia shows the i5 having a bus speed of 2.5 GT/s. Would this be from the QPI then?

If so, what percentage of the bus speed would the RAM use when data is being transferred at the full speed of 1333 MHz?

If I multiply 1333 MHz by 10/8 for the 10b/8b encoding, I get 1.67 GT/s. Would this be the maximum bus bandwidth that would be allocated to the memory?


Here's the wikipedia article that I was referencing: http://en.wikipedia.org/wiki/Comparison_of_Intel_proces...

Thanks
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December 26, 2009 5:01:52 AM

davidd31415 said:
Thanks all. Wikipedia shows the i5 having a bus speed of 2.5 GT/s. Would this be from the QPI then?

If so, what percentage of the bus speed would the RAM use when data is being transferred at the full speed of 1333 MHz?

If I multiply 1333 MHz by 10/8 for the 10b/8b encoding, I get 1.67 GT/s. Would this be the maximum bus bandwidth that would be allocated to the memory?


Here's the wikipedia article that I was referencing: http://en.wikipedia.org/wiki/Comparison_of_Intel_proces...

Thanks


You can learn more from: http://en.wikipedia.org/wiki/Intel_Core_i5
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