CPU-boundedness of the video system Part II – Effect of the CPU cache memory and memory speed
Effect of the memory (RAM) operating speed
In the first part of the review, despite the generality of the posed problem, we used the only platform - the CPU Athlon 64 4000+, a motherboard on the base of the nForce 4 SLI chipset and DDR400 memory running in the dual-channel mode. Of the components listed here, only the CPU clock speed was varied through a reduction of the multiplier, whereas the FSB speed, memory operating speed, and all the other remained unchanged. It is quite reasonable to hear the question - how will the graphs of CPU-boundedness look on change in other parameters? As is known, both the memory operating speed and the CPU cache size affect the performance. So, we'll be examining the extent of their effect effect right now.
You already know the test conditions used in the first part.
Test setup
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Bus
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PCI-Express
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CPU
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MB
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Memory
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OS
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WinXP + SP2 + DirectX 9.0c
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PSU
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Hiper 525W
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We used the method of finding the «line of maximum possible results», that is, for a selected 3D application we set the maximum possible resolution with neither the full-screen anti-aliasing(FSAA) nor anisotropic filtering (AF). In this case, the results are not determined by the video card performance, but the CPU - even by the platform as a whole!
Apart from the already conducted tests of the standard configuration with DDR400 memory set to the dual-channel mode, we produced results for the following configurations:
- Memory speed - DDR400, mode – Single Channel DDR400
- Memory speed - DDR200, mode – Dual Channel DDR200
- Memory speed - DDR200, mode – Single Channel DDR200
Be not confused by some "artificiality" of the mentioned modes for the memory. However strange it sounds, the Single Channel DDR400 mode is quite possible to come across in the home computers of users. The reasons are hackneyed - a single memory module is used for the reason like "will buy one more whenever I get the money", or wrong installation of two memory modules into the memory bank of the same channel. The Dual Channel DDR200 mode looks more exotic, but also can be found sometimes. With 4 memory modules installed, some motherboards automatically reduce the operating speed down to DDR333 or even DDR266 to improve stability. The option of reducing the speed to DDR200 is some sort of an exaggeration, but we simply want to illustrate how the results under such minimum settings will change. The same applies also to the Single Channel DDR200 mode.
The produced results are depicted on the following graph.
What conclusions can inferred from this graph? As it turns out, more important is the memory operating speed but not the number of channels! The single-channel DDR400 mode is more powerful that the dual-channel DDR200, although the maximum theoretical bandwidth in both cases is the same. Needless to say, the lowest results are demonstrated by the single-channel DDR200 memory. But what is interesting, the platform with DDR400 Dual Channel memory is different from the platform with Single Channel DDR200 memory at the maximum memory bandwidth as much as by 4 times, but the difference in results (for the same CPU clock speed) turns out to be at the level of merely 50%, that is, by 1.5 times.
The system with Dual Channel DDR200 memory lags behind the leader by 25%, whereas the system with Single Channel DDR400 – by merely 10%. As regards the other possible types of memory (DDR333 and DDR266), the results of such systems will evidently be between the results of systems with DDR200-DDR400 memory.
That is just the answer to the question as to how the operating mode and the memory speed affect the maximum possible results for a selected platform. We stressed this phrase on purpose, since in reality the demonstrated FPS is normally restricted by the performance of the video card. Assume that under the conditions of our test some video card is able demonstrating no more than 60 FPS, whereas at CPU clock speed exceeding 1400 MHz it turns out that a system with Single Channel DDR200 memory is quite enough to reveal all the capabilities of the video card!
The practical conclusion for thrifty users is - don't be hasty at getting rid of the old DDR266 and DDR333 memory. The RAM capacity is never too much, and it will still be of use for some time.
Now let's move to a more difficult question.
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