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Thread: Front Side Bus




  1. #1
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    When someone refers to "Front Side Bus" and "Bus" are they talking about the same thing?

    How do I calculate the Bus speed on the newer DDR ram that classifies itself as PC2100, etc?

    Thanks.

  2. #2
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    [b]When someone refers to "Front Side Bus" and "Bus" are they talking about the same thing?
    Not necessarily as there is the PCI and AGP bus too amongst others. People should be more specific in what they're talkin' about.
    [b]How do I calculate the Bus speed on the newer DDR ram that classifies itself as PC2100, etc?
    PC2100 runs at 133MHz pure speed but as data is sent at 2 units of data per cycle this becomes 266MHz.
    The 2100 part of the represents the theoretical bandwidth of information that travels thru the memory so it represents 2.1GB/s of bandwidth and PC2700 (166MHz or 333MHz data rate) equals 2.7GB/s of bandwidth. :smokin:
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  3. #3
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    So the PCI and AGP buses can be a different speed than the front side bus? Does the fsb relate to the ram?

  4. #4
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    Front Side Bus is not always in direct relation to RAM, as some motherboards allow a + or - 33Mhz setting for using SDRAM running at other than the Front Side Bus speed of the processor.
    that was common in some of the PIII Motherboards
    The reason a diamond shines so brightly is because it has many facets which reflect light.

  5. #5
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    The PCI is spose to run at 33MHz and the AGP at 66MHz but when overclocking the FSB these will also be raised as they work with dividers off the FSB ( 133/66/33 > overclock> 150/75/37.5).
    The FSB does also relate to the memory which in most cases is equal to the CPU but some chipsets allow the memory to run at 33MHz above the FSB speed (common with later VIA chipsets) but still all is relative just like the PCI/AGP when overclocking using the frontside bus. :smokin:
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  6. #6
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    Was looking over this thread again and thought of something else... My MSI 645 Ultra says that it has a "400 MHz System Bus". What exactly is running at 400 mhz? My fsb is set at 100 mhz, and my ram is 266 ddr, so I'm not sure what the box refers to. Thanks.

  7. #7
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    P4's (and the latest Celerons) use a "quadpumped" data rate mean that 4 bits of info is being transmitted every cycle (or wave length) so every real MHz (100MHz in your case) is then quadpumped to deliver a 400MHz data rate.
    Your DDR SDRAM memory runs a 133MHz real rate one bit of data per cycle but as DDR delivers 2 bits of data per cycle "double pumping" you get the effective 266MHz double pumped rate. :smokin:
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