InfoWorld review: Intel's Westmere struts its stuff

Fast AES encryption, better scalability, and consistent per-core performance make the new six-core Xeon a worthy successor to Nehalem

In the year since Intel released the Nehalem-EP quad-core Xeon CPU, all the hubbub surrounding that chip and its new design has proven accurate. Bigger, better, faster, more -- a whole lot more than anything that Intel had ever released before. But that was then, this is now, and as they say, what have you done for me lately?

Today, the Nehalem-EP gives way to the Westmere-EP, or X5600-series Xeon CPU. Whereas the Nehalem was a big-time performance bump over the previous generation, the Westmere is a more incremental and predictable improvement, but it's definitely a better chip. Westmere picks up where Nehalem left off.

[ Also on InfoWorld: Intel's Westmere and AMD's Magny-Cours will change the face of IT forever. See "Modern multicore and the next generation of IT." ]

The key developments in Westmere-EP are two more cores (six total), the ability to address two DIMMs per channel at 1,333MHz, a 50 percent larger L3 cache, a set of instructions (AES-NI) for accelerating AES encryption, and better CPU power management. Westmere is the equal of Nehalem in single-threaded workloads, but far more scalable thanks to the additional two cores per die. The speed of Westmere's encryption operations will also turn heads.

In fact, the 400 percent performance increase shown with the AES-NI instructions makes whole-disk encryption almost unnoticeable. Previously encryption required a fairly sizable performance trade-off, but with the Westmere's AES performance jump, it becomes a no-brainer. And that's just one of many potential use cases of the AES-NI features.

Generation gap
The Westmere is built on the same basic guidelines as the Nehalem -- integrated memory controller, shared L3 cache per socket, and QPI (QuickPath Interconnect) -- but it's based on a 32nm process rather than Nehalem's 45nm. It runs up to 3.33GHz per core, and two threads per core with Hyper-Threading. That's 24 logical CPUs in a two-socket system, all balanced against 6.4GT/s QPI. It's definitely fast, but not terribly so when compared to Nehalem CPUs running at the same clock speed.

Like Nehalem, Westmere implements Turbo Mode to ramp up the clock speed on certain cores depending on load. Turbo Mode benefits single-threaded and lightly threaded applications by increasing the performance of a few cores when needed.

Also, Westmere CPUs sit in the same sockets as Nehalem CPUs. In fact, some Nehalem-based mainboards can support Westmere already, possibly requiring a BIOS update. This isn't true of all Nehalem systems, however, so do some research first.

In a bid to reduce power consumption, Westmere CPUs can essentially gate off unused cores and shut them down to reduce power, saving their state in cache. Yes, Nehalems can do this too, but Westmere chips can also gate off the uncore, or the region of the CPU that is tasked not with central processing but with memory control and L3 cache, bus controllers, and so on. Whereas a Nehalem could power gate each core, the Westmere can power gate everything, which has the benefit of reducing power draw at idle.

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