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My desktop PC's DDR2-1066 (PC2-8500) RAM memory is running slowly - at the speed of slower DDR2-800 (PC2-6400) memory

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RAM memory problem: Why is my desktop PC's DDR2 RAM memory running slower than it should?

I have built a new desktop PC successfully. [Visit the Build Your Own PC section of this website for information on how to do that.] However, I bought a DDR2-1066 (PC2-8500) RAM memory kit from Kingston (KHX8500D2K2_ 4G) that should run at 1,066MHz. But when I run the CPU-Z utility, it reports that the memory is running at PC2-6400 speeds. That is, at 800MHz instead of 1,066MHz. A PDF document on Kingston's website says:"Each module has been tested to run at 1,066MHz at a latency timing of 5-5-5-15 at 2.2V". How do I get the RAM to run at its correct speed?

Answer

The reason that your PC's DDR2 RAM memory is not running at its specified speed is motherboard compatibility.

In Windows systems, you can only run memory that the PC's motherboard's BIOS Setup Program supports. The BIOS of the motherboard is responsible for the memory settings. To make sure that every PC that supports DDR2 memory boots when the memory is installed, each DIMM memory module is programmed to tell the BIOS that it runs at a common speed that all DDR2-supporting motherboards should support, because some DDR2-supporting motherboards may not support DDR2-1066 (PC2-8500) memory speeds - the highest specification of DDR2 memory, which can run at the slowest DDR2 memory speed of DDR2-400 (PC2-3200) memory. Unfortunately, memory modules don't come with instructions telling you that this is what happens.

You need to boot your PC and enter its BIOS and then locate the memory settings, which vary from one make/model of motherboard to another. The motherboard's user manual that came with the motherboard or which can be downloaded from its manufacturer's website has a section on the BIOS that explains the settings. If necessary, you can use the free CPU-Z utility that you used to find out the memory speed to identify the make/model of the motherboard in the PC.

CPU-Z provides a tab on the memory settings called SPD. You need to override the reported SPD settings for DDR2-800 (PC2-6400) memory and set the speed to 1,066MHz in the BIOS. Note that your motherboard must support the timings and voltage in Kingston's PDF quotes. Your motherboard's user manual's BIOS section will tell you which DDR2 memory it supports. The standard voltage for DDR2 RAM is 1.8V, but your memory requires 2.2V to run at 1,066MHz. That means that you also have to increase the memory voltage in the BIOS, which is a feature that not all motherboards provide. You might find that a lower voltage setting of say 2.1V will do - if that is the maximum voltage that your motherboard's BIOS allows. If you can't increase the voltage, you'll have to leave things as they are, which isn't much of a hardship because DDR2-1066 memory is noticably faster than DDR2-800 memory.

In the BIOS, you should first look for an option to disable the SPD timings, or one that allows the enabling of manual timings. If that can be done, look for a DRAM ratio setting or an option to set the MHz to increase the memory speed to 1,066MHz. Then look for the timing controls, which are usually divided into 'standard' and 'advanced' settings. You should find that the standard timings are in the same order as Kingston's latency timings: 5-5-5-15. In your BIOS, change each of these in turn (where necessary) to the correct values as shown in CPU-Z, instead of leaving them set to Auto. If your BIOS doesn't have these in order, the manufacturers' latency figures refer to: CAS latency, RAS-to-CAS delay, RAS precharge and precharge delay (tRAS). You should leave the advanced timings set to Auto.

Use the BIOS option to save the changes. The PC will reboot. You should find that CPU-Z now reports the modules running at the correct 1,066MHz. The memory speed is called the DRAM Frequency under the Memory tab in CPU-Z. The effective memory speed is twice the motherboard's bus speed, which is reported under the CPU tab, due to the fact that DDR memory is double-data-rate memory, which means that it can use both the rising and the falling cycle of the frequency, which means that the speed is effectively twice the motherboard's bus speed. Standard SDRAM can only use the rising cycle to transfer data, so its speed is the same as the speed of the bus. The FSB: DRAM 1:2 under the CPU tab shows the ratio of the bus speed to the effective memory speed.