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I have this HP Pavilion Desktop. As you can see, that page says the memory speed supported is PC2-4200. It currently has a 512 MB stick - CPU-Z Screenshots:

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However, a scan gives a slightly different report - It says the system can support PC2-5300 memory.

So my question is which one should I trust? I want to upgrade the computer's ram to 2 GB (the maximum supported), because XP Media Center is giving me problems and I will install Windows 7 on this. PC2-6400 is the most common DDR2 memory I have been able to find here in the market. Will it cause any problems if I install 2 × 1 GB PC2-6400 DDR2 memory sticks (in dual channel) in this computer, (afaik, it will just run at the lower speed of 533 MHz, or whatever the motherboard supports), or do I absolutely need to get PC2-4200 sticks?

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CPU-Z is showing what is installed. Chipsets usually support more than one speed within a technology. – Richard Apr 8 '10 at 8:54

A rather comprehensive answer from


If you are intending to use a faster memory module in your computer, here is a summary of the items to consider before purchasing and installing it:

  • The memory has to be of the same technology (DDR, DDR2 and DDR3 are not cross compatible)
  • The PC must support the memory module densities being considered
  • No unsupported features like ECC must be present on the module
  • The memory will only be as fast as that supported by the memory or as slow as the slowest installed memory module

The answer to this question really is yes and no. If you are talking about a computer for example that uses DDR and you want to use DDR2, it will not work. They use two different clocking technologies that are not compatible within a system. Now, if you are looking at the same type of memory as what is already in the system, then you can buy memory that is faster than the existing memory. Of course, there are always restrictions.

In order for this to work, the memory modules must be of a density that is supported by the computer motherboard. For example, a system that can support 1GB modules cannot use a faster 2GB memory module as the system will not recognize it. Similarly, if your motherboard won't support memory with ECC, it won't support faster modules if they have this feature.

The other issue has to do with the speed. Even though they may be faster modules, they will not be running at the faster speed. This can happen in two cases. The first is that the motherboard or processor will not support the faster memory speed. When this happens, the modules will instead be clocked at the fastest speed that they can support. If the modules are installed with some slower ones already installed, the memory system will run at the slowest memory timings and speed.

So, why would you want to install faster memory in a system if it will still run at the slower speed? It has to do with availability and pricing. Often times as memory technology ages, slower modules may drop out of production leaving only faster ones available. Such might be the case with a system that supports PC2700 DDR memory but all you can find is PC3200 DDR modules. Memory is considered a commodity and as a result has variable pricing. This can result in situations where a faster memory module might be less expensive than a slower one. If PC2-5400 DDR2 supplies are tight, it might be less expensive to buy a PC2-6400 DDR2 module instead.

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