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  1. #1
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    Curious about memory chip DDR2-667 relative to bus clock 1066 megahertz

    I am servicing a Dell OptiPlex 755 SFF computer that had mismatched memory: 2 chips - a Dell branded 2GB chip that is single sided and an aftermarket 1GB double-sided chip that was added by the previous owner. The computer runs ok but the user always had to press F1 when booting up. I removed the aftermarket chip so the computer runs only with the original Dell 2GB chip as I am not a fan of running with mismatched memory. The OS was XP Pro and the computer has been upgraded to Win7 Enterprise

    I checked out crucial.com since I've never had any issues with ordering from them. They recommend part CT722555/DDR2-667 which is fine with me.

    However my question is this; according to Belarc, the system board Bus Clock is 1066 megahertz
    --- Are the DDR2-667 relative to the Bus Clock of 1066 megahertz factors to consider when buying memory?
    --- In other words does the memory configuration affect the Bus Clock of 1066 megahertz?

    I did check Dell's website using the computers service tag number and they indicated either 667 or 800 memory chips but 667 is recommended for units that max out at 4GB memory and Crucial does report the computers max memory is 4GB so I would be ok ordering Crucial's recommendation. But I'm still curious about the effect of memory configuration of 667 relative to the Bus Clock of 1066 megahertz

  2. #2
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    Memory speed is a function of FSB speed, with a faster FSB able to move data faster, so you need faster RAM to keep up. Basically you double the FSB speed to get the required RAM speed - in your case a 333MHz FSB would require 667MB/s RAM, otherwise known as PC2-5300. Faster RAM is really just wasting money unless you are overclocking.
    See the DDR2 section on this crucial page.

    cheers, Paul

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    cmptrgy (2015-01-10),Dennis Wright (2016-03-08)

  4. #3
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    I've also noticed on Crucial that they tend to drop the slower speed modules in favor with faster that is backward compatible, i.e. upgrading a computer that came with DDR2/PC2-4200 requires buying DDR2/PC2-5300 modules. But then not many upgrade their RAM until it's needed for productivity, my first computer and first upgrade of it was going from 4MB to 8MB because WordPerfect 5.1 for Windows [on Win3.1] kept having to use the Swap File when typing more than 6 or 7 pages. I was questioned by a tech as to the need for 8GB when 4GB would do on my new Win7 computer a few years ago and wouldn't you know it, she put 8GB in her next computer [we had worked together in a shop for a few years].

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  6. #4
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    het Paul, excellent article

  7. #5
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    For Christmas my granddaughter received a brand new TOSHIBA Satellite C55-B PSCMLU-03601M Windows 8.1 laptop and runs like crap
    --- She has a terrible time when using Facebook & Youtube videos which she does a lot
    Belarc reports a Bus Clock: 83 megahertz (Board: TOSHIBA ZBWAA 1.00 Bus Clock: 83 megahertz)

    The computer does have 4GB RAM but when I saw the bus clock of only 83 megahertz I looked up crucial and DDR3 PC3-12800 1600Mhz is recommended. Without physically checking the installed chips, I do not know what it has and I’d have to get the computer back in order to do so but we live about 60 miles apart and I’d like to ask the following question at this time

    Isn’t the bus clock of 83 megahertz much too low even if the installed memory chips are DDR3’s?

  8. #6
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    83MHz sounds like Belarc has the wrong end of something.
    Open Task Manager and click on the Performance tab. This will show you CPU speed, which should give a clue to bus speed by dividing by 8. Using the example in post 2, a 333MHz FSB would run the CPU at 2664MHz, with 667MHz RAM.
    See this Wikipedia article.

    cheers, Paul

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