Intel QPI speed relevancy

QPI replaces the old FSB architecture and changes the way the CPU communicates with the RAM memory. QPI is inspired by AMD's imc called HyperThreading, and replaces the old FSB architecture with a direct connection to the RAM.

Faster versions may offer more memory bandwidth, but it depends on your applications whether this will benefit overall performance in a meaningful degree. The biggest change comes from having QPI instead of having FSB, just some more GT/s will make workloads like rendering faster, and other memory-hungry workloads.

Ah yes meant HyperTransport, confusingly both can be called HTT. Though QPI and HyperTransport are technically not alike, the motivation for Intel to do it and the need to hurry with it was clearly prompted by AMD, same with integrating AMD64 spec; if it had been Intel's choice it would have taken much longer before consumers were having 64-bit systems.

QPI is the interconnect between CPU and the northbridge (which at this point is just a glorified PCIe hub and passthrough to the southbridge when you're in uniprocessor mode) . It has essentially nothing to do with RAM in the conventional sense*. The on-die memory controller on the CPU != QPI.




* You could be pendantic and say that QPI carries information from the memory to the PCIe and other I/Os, but typically memory throughput between the CPU and the DIMMS is the relevant metric.

Sorta.

You need to think of QP more in terms of a "link data rate" than speed (it's a silly distinction but bear with me).

The old Intel FSB theoretical max was 1.6 GT/s - a 'quad-pumped' single bi-directional 400MHz bus. The old FSB was starting to become a bottleneck. ""GT/s"" simply measures the theoretical bandwidth across the CPU interconnects to the rest of your system.

QP interconnects consist of multiple parallel links which are faster but the increase in speed you are seeing is from higher bit rates/transfers across a 'wider bus'.

When you think of QP it is better to think of theoretical bandwidth --- with all things being equal in your rig a 'larger' theoretical QP rate will not necessarily be faster if you are not 'starving for bandwidth' in the first place.

They way we looked at it with AMD, as long as your HT rate exceeded your memory 'rate' you were good to go (pretty simplistic but I think you get the point). I assume it is pretty much the same with QP with a few other minor distinctions.

And I will also assume that Intel (like AMD) will see a greater gain in performance (increased bandwidth and reduced latency) from increasing the speed of the integrated memory controller --- I haven't tested it and don't really know but that would be a decent 'edumacated' guess ...