Memory subsystem performance

This bit of geeky goodness gives us a peek into the cache hierarchy of each chip at various block sizes to see how much bandwidth is available. Not surprisingly, the Lynnfield Core i5-750 and Core i7-870 look very similar to the Core i7-975, only a bit slower. They also look more similar to the Phenom II, with its three-level cache hierarchy, than to the Core 2 Quad Q9650, with its large L2 caches and no L3.

The CPUs sort themselves out pretty clearly by socket type here. Notice how close the Lynnfield processors, with dual channels of 1333MHz memory, come to matching the Core i7-920 and 950, with three channels of 1066MHz RAM. The Phenom II, which also has dual channels of DDR3 at the same clock speed and timings, can't quite match the Lynnfield chips in measured throughput. The poor old Core 2 is limited by its front-side bus and can't reach half the bandwidth the Lynnfield chips deliver.

Having only two channels of memory actually gives the Lynnfield processors an advantage in access latencies over the Core i7-900 series. Even the Core i7-975 Extreme, with which we used 1333MHz memory, isn't as quick to memory as the Core i5-750 and i7-870. Once again, the Lynnfield memory subsystem outperforms a very similarly configured Phenom II, as well.

Now, we'll take a closer (and gratuitously indulgent) look at access latencies across the board with our ridiculous 3D graphs.

All told, the Lynnfield chips have some of the lowest access latencies we've ever measured in a processor. Interesting fact: we measured the Lynnfield chips' L1 cache latency at three cycles, whereas the Bloomfield Core i7 L1 caches measured consistently at four cycles. Also, Lynnfield L2's latency was eight cycles, while Bloomfield's was 11. I believe L3 latencies are best left in nanoseconds as we've reported them in the graphs above, since L3 cache speeds are independent of core clocks.