So, why would someone buy these modules? Someone would buy them for overclocking. Why should or shouldn’t you buy these modules? So, they won’t automatically run at 2,133 MHz nor automatically achieve the 17,000 MB/s transfer rate. ![]() ![]() If you install it on a regular PC system supporting DDR3 RAM memories, they will probably run at 1,333 MHz (DDR3-1333) – which the maximum DDR3 RAM standard speed –, achieving a maximum transfer rate of 10,664 MB/s (or 21,328 MB/s if they are running under dual channel mode, read our tutorial on dual channel to understand more about this subject). This is the maximum clock rate they support, not the clock rate at which they will be running. Even though they are labeled as DDR3-2133, they won’t run at 2,133 MHz automatically on your system. How do RAM memories work?įor example, let’s say that you bought a pair of DDR3-2133/PC3-17000 RAMs. Actually, this is a very common misjudgment. If the memory module is installed on a system where the memory bus is running at a lower clock rate, the maximum transfer rate the memory module will achieve will be lower than its theoretical maximum transfer rate. Maximum Theoretical Transfer Rate = clock x 8 As 64 / 8 equals 8, we can simplify this formula to: Since DIMM modules transfer 64 bits at a time, “number of bits” will be 64. Maximum Theoretical Transfer Rate = clock x number of bits / 8 The maximum transfer rate for a memory module can be calculated through the following formula: How to calculate the maximum transfer rate for a memory module?įigure 1: A DDR3-1333/PC3-10666 memory module Pay attention to the RAM timings (7-7-7-18) and voltage (1.5 V). In Figure 1, you can see a PC3-10666 memory module, which uses DDR3-1333 memory chips. The first classification, DDRxxx, is the standard used to classify memory chips, while the second classification, PCyyyy, is the standard used to classify memory modules. As you can see, we use the number “2” or “3” after “DDR” or “PC” to indicate that we are talking about a DDR2 or DDR3 memory, not DDR. And DDR3-1333 memories can transfer data at 10,664 MB/s and they are labeled as PC3-10600 or PC3-10666. DDR2-800 memories transfer data at 6,400 MB/s and they are labeled as PC2-6400. DDR400 memories transfer data at 3,200 MB/s at the most, and hence they are labeled as PC3200. The second number indicates the maximum transfer rate that the memory reaches, in MB/s. ![]() Therefore DDR400 memories work at 200 MHz, DDR2-800 memories work at 400 MHz, and DDR3-1333 memories work at 666 MHz. The real clock of the DDR, DDR2 and DDR3 memories is half of the labeled clock speed. It is important to note that this is not the real clock speed of the memory. For instance, DDR400 memories work at 400 MHz at the most, DDR2-800 can work up to 800 MHz, and DDR3-1333 can work up to 1,333 MHz. The first number, xxx, indicates the maximum clock speed that the memory chips support. How to understand the RAM classifications? The first classification By the way, if you are interested in knowing the difference between DDR, DDR2, and DDR3 RAM memories, read our tutorial on this subject. In this tutorial, we will explain exactly what each one of these RAM Timings means.ĭDR, DDR2, and DDR3 Ram memories follow the DDRxxx/PCyyyy classification. DDR, DDR2, and DDR3 RAM memories are classified according to the maximum speed at which they can work, as well as their timings.
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