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Part 2: How Many CPU Cores Do You Need?

Part 2: How Many CPU Cores Do You Need?

A few months ago, we looked into the effectiveness of using different numbers of CPU cores with various types of software. We received a lot of good feedback from that article, and there were some interesting suggestions from the community that we've taken to heart in this follow-up.

Primarily, there was a concern that part one might have been flawed technically, as the Core 2 Quad Q6600 we used in our testing does not share all 8 MB of its L2 cache between its four CPU cores. Intel's Q6600 instead has two separate 4 MB cache repositories, each shared between one pair of CPU cores. This means the quad- and triple-core results would have demonstrated the CPUs utilizing 8 MB of total cache, while the dual- and single-core results show that they were likely benefiting from 4 MB. Indeed, the benchmarks may have been reflecting the difference in L2 cache availability more than performance attributable to enabled processing cores.

To remedy this, we are using a different CPU this time around: AMD's Phenom II X4 955 BE. There are a number of reasons why the Phenom II is ideal for these tests. First of all, its 6 MB of L3 cache is shared between all four CPU cores, so the cache's impact on results will be kept to a minimum. Secondly, since there are now X2, X3, and X4 versions of the Phenom II CPU based on the same die, we will have the opportunity to test the validity of the method we use to simulate fewer CPU cores. By comparing simulated results to an actual retail CPU with fewer CPU cores, we will know more definitively whether disabling CPU cores in the operating system is a truly legitimate test.

At the end of these tests, we will be able to compare the Phenom II X4 results with the ones achieved by Intel's Core 2 Quad Q6600 to see if the impact of shared CPU cache is dramatic or minimal.

A few readers were also interested in simulating a scenario where multiple applications are running at the same time, in order to gauge the benefit of additional CPU cores while multitasking. We therefore ran a new test to analyze this type of scenario, too.

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  • 1 Hide
    redkachina , 4 August 2009 03:08
    great..I was waiting for this one..
  • -1 Hide
    the Innocent , 4 August 2009 07:09
    This why I went with the Q6600 I do more than one thing at a time.
  • 0 Hide
    BrightCandle , 4 August 2009 07:38
    I am so glad you finally did this test. With dual cores having an advantage of 25% clock speed its actually now apparent that for gamers dual cores are the better option - cheaper and faster.
  • 1 Hide
    avatar_raq , 4 August 2009 23:20
    Putting core i7 aside, those charts show that dual cores are the most attractive for gaming,plus they tend to have lower prices and higher clocks than quads, add better and easier overclockability on top of that, not to say lower power consumption (in general), and the choice seems no brainer, for all but the most spoiled gamer!
    Nice article..
  • 3 Hide
    papalarge123 , 5 August 2009 03:49
    i dont believe that the dual cores are the way to go/best choice for gaming, as software from this point on will be callibrated for quads or above,

    it clearly shows an improvement from dual to triple or even quads, and if most people are like myself when it comes to computing and gaming, pulling the best out of the system from the budget available, then the triple and quad core cpu's sure look better than the dual cores.

    also down to price and overclocking ability, then the quads from intel can reach virtually the same speeds as the duals and with only a small price difference, making a better price to performance gain overall.
  • -3 Hide
    goozaymunanos , 5 August 2009 21:47
    why are they only showing gaming benchmarks at 1024x768?

    i'm a bit behind the curve and even i'm playing at 1680x1050?


    p.s. stuff and nonsense:
  • 3 Hide
    chispa , 6 August 2009 16:39
    @goozaymunanos I think it's because the higher resolutions stress mainly the video card, while this test was to highlight the differences in the processors. Thus the video card was stressed as little as possible to allow the processor differences to shine through.
  • 0 Hide
    lekiamiga , 6 August 2009 23:32
    but that makes the game benchmarks basically synthetic as gamers wont be running at those low resolutions and low gfx levels on new hardware.

    They should do gaming benchmarks at high deatails so i know how much of a difference a quad cpu will really make on the games.
  • 0 Hide
    Anonymous , 10 August 2009 18:17
    Nice, I already ordered 955 :)  Can't wait for it.
  • 0 Hide
    Anonymous , 15 August 2009 06:53
    Am I the only one quite disappointed with the results? :( 
    I expected far better performance from dual / quad cores than a single core - basically like running multiple processors.

    So I was expecting twice the performance with dual cores, and 4-times the performance with 4 cores.
    I guess this might be expected where the processors were using dedicated caches?

    Perhaps it also reveals that Windows isn't correctly taking advantage of the power of 2-4 cores - i.e. the kernel isn't too intelligently dividing multi-threaded / multi-apps capability to multiple cores.
  • 0 Hide
    Anonymous , 18 August 2009 01:54
    I thought the question was mostly "Which applications really benefit from more than 2 cores?" anyway?

    Would be interesting to see a benchmark with Supreme Commander since that's meant to be a well threaded game, and really needs CPU performance when a large number of units are in the game.

    Another application which can really use multiple cores is software compilation (e.g. try compiling a kernel with the option: -j 4). But since the compiler itself is not (normally) threaded, but just run several times in parallel, clearly the performance increase is linear.
  • 0 Hide
    Anonymous , 19 August 2009 01:21
    I suspect differences may be even more apparent on a Linux system than with a MSoft OS. Generally, Linux kernels multi-task more transparently amd should lend themselves to multi-threaded multi-processor tasking more efficently.
  • 0 Hide
    wild9 , 22 August 2009 23:29
    avatar_raqPutting core i7 aside, those charts show that dual cores are the most attractive for gaming,plus they tend to have lower prices and higher clocks than quads, add better and easier overclockability on top of that, not to say lower power consumption (in general), and the choice seems no brainer, for all but the most spoiled gamer!Nice article..

    That's why the socket AM3-based Athlon II/Phenom II x2 seem so appealing, considering their cost. Not saying Core 2 is bad, either, just that I have some Socket AM2 stuff lying around and for a relatively cheap price these deliver killer blows for games, as well as provide a very good overclocking potential. Most of my clients have AMD's due to price restrictions but I have no complaints and at least I know that when I install these parts they're gonna run cool and fast.
  • 0 Hide
    tygrus , 3 September 2009 20:39
    And what happens when data intensive tasks run out of RAM or disk I/O. We need faster storage.
    We still need faster fingers and eyes to go with the faster computers.