Windows 7's killer feature: Windows on multicore, redux

Running heavy multitasking workloads on advanced multicore hardware, Windows 7 finally surpasses leaner Windows XP

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Of course, the proof, as they say, is in the pudding. And while Microsoft stated from the beginning that Windows 7 would be better able to leverage the new generation of multicore systems than Windows XP, validating this claim has proven to be easier said than done. For starters, few current-generation PCs sport the necessary combination of cores and NUMA-like processor interconnects that allow Windows 7 to strut its multicore stuff. In fact, the benchmarks I ran in support of my previous article on the subject showed Windows 7 falling well behind XP on everything from a dual-core desktop PC to a quad-core mobile workstation -- hence, my conclusion that Windows 7's advantages on multicore wouldn't be a factor until 16- or 32-core systems became commonplace.

Fortunately, I now know better. Not only is Windows 7 well positioned to leverage the coming generation of many-core PCs, it's capable of delivering tangible advantages today, using current-generation mainstream (though expensive) hardware. My revised benchmark tests, which include data from the aforementioned 8-core (16-thread) Z800 workstation, show Windows 7 blowing past XP on a mixed, multiprocess workload consisting of a SQL database (47 percent faster), MAPI workflow (178 percent faster), and multimedia playback tasks. (See "How I tested" for details.)

[ Graphics-intensive benchmarks under Windows XP, Windows Vista, and Windows 7 on a quad-core workstation show mixed performance results and the superior power efficiency of Windows 7. See "Windows 7 on multicore: How much faster?" ]

When viewed in terms of percentage scalability, moving from 4 cores on a single CPU to 8 cores spread across two CPUs yielded a much greater improvement under Windows 7 than Windows XP. The SQL database task showed an overall improvement of 72 percent under XP versus a 200 percent boost under Windows 7. Likewise, the MAPI workflow task, which showed negligible (4 percent) improvement under XP, jumped by nearly 360 percent when moving from 4 to 8 cores.

All in all, it's a significant victory for Windows 7, one I attribute to the newer OS' more refined support for multicore CPUs, simultaneous multithreading (SMT, aka Hyper-Threading), and NUMA. That Windows 7 was able to accomplish this much at the 8-core level -- overtaking XP, then pulling away by a wide margin -- came as a pleasant surprise, one that deepened my respect for the Windows kernel development team. These guys really know how to wring the most of the underlying hardware platform.

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Windows on multicore: Scalability (2 to 4 cores)

Database Messaging workflow
Windows XP 265 percent
32 percent
Windows Vista 492 percent 58 percent
Windows 7 571 percent 15 percent

Windows on multicore: Scalability (4 to 8 cores)

Database Messaging workflow
Windows XP 72 percent 4 percent
Windows Vista 143 percent 267 percent
Windows 7 200 percent 358 percent
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