Since the primary target platform for the above discussed memory kits is Ivy Bridge + Intel Z77, we will test 32 GB G.Skill kits consisting of four 8 GB modules each in an LGA 1155 system built on Asus P8Z77-V Deluxe mainboard. Since overclocking memory modules reviewed today are primarily purchased by enthusiasts, we also used Intel Core i5-3570K processor overclocked to 4.5 GHz.
As a result, the complete list of hardware and software components in our testbed looked as follows:
- CPU: Core i5-3570X, overclocked to 4.5 GHz (Ivy Bridge, 4 cores, 6 MB L3);
- CPU cooler: NZXT Havik 140;
- Mainboard: ASUS P8Z77-V Deluxe (LGA 1155, Intel Z77 Express);
- G.Skill Ares F3-1333C9Q-32GAO (4 x 8 GB, DDR3-1333, 9-9-9-24);
- G.Skill RipjawsX F3-1600C9Q-32GXM (4 x 8 GB, DDR3-1600, 9-9-9-24);
- G.Skill Sniper F3-1866C10Q-32GSR (4 x 8 GB, DDR3-1866, 10-11-10-30);
- G.Skill RipjawsZ F3-2133C9Q-32GZH (4 x 8 GB, DDR3-2133, 9-11-11-31);
- G.Skill TridentX F3-2400C10Q-32GTX (4 x 8 GB, DDR3-2400, 10-12-12-31).
- Graphics card: Nvidia GeForce GTX 680 (2 GB / 256 bit GDDR5, 1006/6008 MHz);
- Drive: Intel SSD 520 240 GB (SSDSC2CW240A3K5);
- Power supply unit: Corsair AX760i (80 Plus Platinum, 760 W);
- Operating system: Microsoft Windows 7 SP1 Ultimate x64;
- Intel Chipset Driver 22.214.171.1246;
- Intel Management Engine Driver 126.96.36.1998;
- Intel Rapid Storage Technology 188.8.131.523;
- NVIDIA GeForce 314.09 Driver.
Configurations with 4 x 8 GB Memory Kits: Closer Look
Before we get down to testing the memory kits described above, we want to dwell upon general issues of using dual-channel kits consisting of four 8GB modules. Although we wrote above that the Ivy Bridge memory controller can easily support such configurations, there are some nuances you should be aware of.
First of all, not all operating systems are ready to support 32 gigabytes of system memory. Of course, you need a 64-bit OS because 32-bit ones cannot access more than 4 gigabytes of address space. Besides, certain 64-bit Windows versions have specific limitations. For example, Windows 7 Home Premium supports only 16 GB whereas Windows 7 Home Basic, 8 GB. Windows 8 has no such limitations, supporting at least 128 GB of system memory in each of its versions.
Second, it's not correct to say that Ivy Bridge CPUs are indifferent to whether you have four or two memory modules. Clocking the memory bus at a high frequency may require your lowering the Command Rate parameter. So if the mainboard has only two DIMM slots filled in, the memory subsystem nearly always can work at Command Rate = 1T. With four modules installed, you can only choose 1T at speeds up to DDR3-2000 inclusive. Faster memory configurations will call for Command Rate = 2T.
The Command Rate parameter isn’t crucial, though. It can often be disregarded completely. Describing the latency between receiving and decoding addresses and instructions, it helps eliminate potential access errors at high loads on the memory controller. Its effect on memory performance is very low. Comparing two memory configurations – two modules with Command Rate 1T and four modules with Command Rate 2T – we can find the second to be even faster as it includes more memory banks.
It is easy to illustrate with tests we carried out using the 32GB DDR3-2133 SDRAM kit RipjawsZ F3-2133C9Q-32GZH. First, we ran it at its default timings of 9-11-11-31-2T and then we took only two modules and improved the timings to 9-11-11-31-1T. Here are the results:
As you can see, the two configurations are very close to each other in performance. So, there is no reason to worry about having to set Command Rate = 2T with four memory modules. The internal organization of the 4-piece memory subsystem makes up for that.
Yet another peculiarity of 4-piece 32GB memory kits is that they generate quite a lot of heat. We used to say that heatsinks for DDR3 modules are largely just a decorative element, but they are actually necessary for overclocker-friendly kits made of four 8GB modules. Such modules have a lot of chips and are located close to each other on the mainboard, inhibiting the natural convection of air. As a result, the temperature may rise very high. So, it's good to have heatsinks, especially with advanced finning, on such memory modules.
The heatsinks must not be too tall, however. When you fill in all of your mainboard’s memory slots, the one nearest to the CPU socket is going to be covered by the CPU cooler. So, the latter should be able to hang above the memory modules without pressing against their heatsinks. The list of compatible CPU coolers shrinks considerably when the memory modules have a total height of over 40 mm.