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pbz
Asked: 2009-05-05 09:08:16 +0800 CST

DDR II 667 vs DDR 400

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We currently have DDR II 667 RAM on the dedicated server. We're looking to a new server. One of the options only comes with DDR 400 (or DDR 400 registered). Is there a big difference between DDRII 667 and DDR 400? This is for an AMD Opteron 170 or Opteron 248.

Also, if I run CPUZ on the current server it reports the type of memory to be DDR (not DDRII) with a DRAM frequency of 200MHz, CAS Latency 3 clocks, RAS to CAS delay 4 clocks, RAS precharge 4 clocks, cycle time 8 clocks, banks cycle time 12 clocks, command rate 1T, DRAM Idle Timer 16 clocks. Does this match the DDRII 667 that we are supposed to have?

Thank you.

central-processing-unit memory

5 Answers

  1. Best Answer

    See question #4 of the page for CPU-Z to see why it might misreport what RAM you have installed. If you eyeball your RAM, most RAM sold in recent years has a sticker on it that says exactly what speed it is.

    You said that CPU-Z reported your memory as:

    • DRAM frequency of 200MHz
    • CAS Latency 3 clocks
    • RAS to CAS delay 4 clocks
    • RAS precharge 4 clocks
    • cycle time 8 clocks
    • banks cycle time 12 clocks
    • command rate 1T
    • DRAM Idle Timer 16 clocks

    Of these numbers, the two with the biggest single impact on memory access speed are the first two above, the front side bus speed (200 MHz x 2 for DDR = 400 MHz) and CAS latency. However, you asked does this mean you don't have DDR-II 667 -- this depends on whether or not your CPU supports a front side bus rate of 667.

    In a comment, you said that this is a server you can't power off or reboot to do this check. So in CPU-Z, look at the SPD tab. SPD (Serial Presence Detect) is a way to read information about the memory from the memory. This should tell you the manufacturer, model, part number, max bandwidth, allowed timings for different bus frequencies, and so on. You can look at each memory slot and tell what kind of memory is in each position.

    In CPU-Z in the "Memory" tab, it just tells you how the BIOS and OS decided to configure memory timings, based on looking at all of the memory chips and based on BIOS configuration. The "SPD" tab tells you exactly what the memory sticks you have are capable of.

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  2. 667 and 400 indicate the bus speed of the RAM; higher is better.

    Then there's also the issue of DDR vs. DDR2; DDR2 is better.

    When it comes to latency, the first number (CAS latency) is the more important of the four numbers; lower is better.

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  3. What kind of server is this? Seems terribly slow. DDR(1) is more expensive than DDR(2) these days if its a new server you should look at the mainanace costs but wow I think I throw away worse pc's than that without looking twice..

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  4. It is also important to note the Front Side Bus speed of the processor. If the FSB is 400 then 667 memory will do you no good.

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  5. The speed difference will be absolutely nil. Even in applications like games that are sensitive to memory bandwidth, there's little if any real-world difference between DDR-400 and DDR2-667, because of DDR2's increased latency.

    You don't mention what the server is doing, but typical server tasks (web, mail, database, etc) are CPU- and/or network bandwidth- and/or IO-bound. Memory bandwidth makes little or no difference for those tasks. The bandwidth of DDR2-400 is something like 3.2GB/sec and unless your server is part of a render farm or is doing certain kinds of science work, you're simply not throwing around anywhere near that much data per second. Unless you've got a fairly pricy SAN or SSD array, your drives can't even hope to read or write 320MB/sec per second, and that's only 10% of DDR-400's bandwidth.

    As others have said, DDR2 is cheaper at this point, so it certainly has that going for it. Just don't expect any performance increase from it.

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