Underclocked DDR

Discussion in 'CPU, Motherboards and Memory' started by marin, May 13, 2006.

  1. marin

    marin Geek Trainee

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    I have a 2GHz celeron on a i845GL based motherboard with a memory controller of 266MHz supporting 266 & 200MHz DDR but actually, the RAM runs only at 200MHz, even if I set the frequency to 266 in the bios. Benchmarking software report a bandwidth only touching the 1200 MB/s and a theorical maximum of 1600. I have 2 x 256 MB sticks(1xDDR333 and 1xDDR400) and every single or double combination of these does not increase the theorical bandwidth to 2100 MB/s and frequency to 266 MHz. I'm getting frustrated, what can be wrong there?!
     
  2. Big B

    Big B HWF Godfather

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    There's nothing wrong, but you should remember that the 1.6GB/s is theoretical. They are most likely a burst rate, not sustained. My PC3200 RAM does just under 2GHz/s. The 3.2GB/s is the maximum throughput, but typically, you're not going to find sustained speeds even close to that.

    I'm not 100% sure on this, but I don't believe the i845 chipsets support asynchronous memory:fsb ratios, however, that's likely why you're unable to run the RAM at 266MHz (or even 333). There may also be certain restriction's placed on the i845GL chipset itself, given it's more budget orientation.

    Third, I believe your Celeron uses a 400MHz FSB, which is derived from a quad-pumped 100MHz bus. This correlated to the PC1600DDR, which has a base frequency of 100MHz.

    Again, there's nothing wrong with the hardware. You may also see different results from different programs, but I doubt you'll see close to the PC1600 speeds simply because of what's being used as far as the OS and any open programs. Even removing them, you still need to understand that the sustained transfer rates are generally noticeably lower than the peak theoretical rates.
     
  3. marin

    marin Geek Trainee

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    Thanks! I didn't think of the 400 MHz FSB but now that I am thinking, 1x100, most brobably is that. Maybe it can go with a celeron D and the board should recognize it as (it practically is) an older P4.
     
  4. Big B

    Big B HWF Godfather

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    Not sure. You'll want to find out if the Celeron D's are supported. They use the Prescott core, and that wasn't designed with Socket 478 in mind. A lot of motherboards do not cope well with that core because of the power requirements.
     

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