Articles: Memory

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Testbed and Methods

In this review we use a modern LGA1150 mainboard with Intel Z87 chipset, installing a Haswell-based Core i5-4670K processor. The focus of our testing is on the high-speed [TridentX] F3-2933C12D-8GTXDG memory kit from G.Skill.

Here is the full list of our testbed components:

  • Processor: Intel Core i5-4670K (overclocked to 4.4 GHz, Haswell, 4 cores, 6MB L3 cache)
  • CPU cooler: NZXT Havik 140
  • Mainboard: Gigabyte Z87X-UD3H (LGA1150, Intel Z87)
  • System memory: 2x4GB, DDR3-2933 SDRAM, 12-14-14-35 (G.Skill TridentX F3-2933C12D-8GTXDG)
  • Graphics card: Nvidia GeForce GTX 780 Ti (3 GB/384-bit GDDR5, 876-928/7000 MHz)
  • Storage: Intel SSD 520 240GB (SSDSC2CW240A3K5)
  • Power supply: Corsair AX760i (80 Plus Platinum, 760 W)

We carry out our tests in Microsoft Windows 8.1 Enterprise x64 with the following drivers:

  • Intel Chipset Driver
  • Intel Management Engine Driver
  • Intel Rapid Storage Technology
  • Nvidia GeForce Driver 334.89

Take note that we overclock our Haswell-based CPU to 4.4 GHz. This ensures higher performance and highlights the correlation between performance and memory subsystem parameters.

Frequency vs. Timings

When it comes to choosing the right type of memory, you often find yourself choosing between higher clock rates and lower timings. This time around, however, we will not carry out detailed tests of DDR3 SDRAM modules with different timings. The fact is that with each new platform memory timings influence overall performance less. So today, the clock rate of DDR3 SDRAM has a much stronger effect than its timings.

There are two reasons for that. First, the minimum latency increases anyway along with memory frequency, so timings adjustments get relatively smaller. Increasing timings by 2 from a minimum of 3 or 4 (as with DDR2 SDRAM) and from a minimum of 9-10 (as with high-speed DDR3 SDRAM) means that the latency increases by 50-70% in the first case and only by 20-22% in the second case. So different combinations of timings do not actually differ much with today's memory. Moreover, the multi-level caching and data pre-fetch algorithms implemented in modern CPUs mask the real memory latency, making its bandwidth more important.

In fact, the manufacturers of overclocker-friendly memory kits have long realized that there's no need to achieve extremely low timings with DDR3 SDRAM. Products with latencies of 7 or 8 cycles have disappeared so it is hard to find DDR3 SDRAM modules with a CAS Latency of less than 9 or 10. But there are more and more products with very high clock rates and high timings.

To prove our point, we carried out a practical test to compare the real-life performance of identical Haswell-based configurations with DDR3-1600 and DDR3-1867 which had different memory timings.

The charts are most illustrative. Increasing the memory frequency by 266 MHz turns out to be far more effective than lowering all timings by 3 to 4 cycles. Even when it comes to real-life latency, which is heavily influenced by timings, DDR3-1867 with rather high timings of 10-10-10-29 turns out to be better than DDR3-1600 with aggressive timings of 7-7-7-21. Comparing the effective bandwidth, DDR3-1600 is always inferior to its higher-speed opponent.

Summing it up, we can see that memory timings have become a negligible factor for modern computers, so you should first look at the clock rate of your DDR3 SDRAM whereas a low CAS Latency and other such parameters have but a small effect on actual performance. The same goes for overclocking. You should first try to make your DDR3 SDRAM work at higher clock rates and only then minimize your memory timings.

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