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Processor Bus Speeds explained

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Article Summary: This article provides information on "Processor Bus Speeds explained".


Table of Contents:
  1. What is processor bus speed & how is it determined
  2. Examples of processor bus speed computation
 
1.    What is processor bus speed & how is it determined    

The bus speed on Precision systems is based on 2 factors:

  • Processor
  • RAM

    Using the Precision Workstation T5500 as an example. This system offers the Xeon E55XX class processor (Nehelem) in single or dual configurations. These are all quad core except the E5502. The processor chosen will determine the front side bus speed.

    When choosing a processor for systems on www.dell.com, there is a "Help me choose" link.  You can use this tool to help you understand the choices available in the system you are reviewing.

    SLN245499_en_US__11391696985654.processor

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    2.   Examples of processor bus speed computation    

    Using a Xeon E5506 as an example, it has a front side bus (FSB) ratio of 4.8. The standard clock multiplier for these systems is 166.67 Megahertz (MHz). When you multiply the two, you should come up with 800.16, so 4.8 x 166.67=800MHz which is what will show for Memory speed in the system BIOS for this processor.

    The Xeon E5550. It has a FSB rating of 6.4. 6.4 multiplied by 166.67 equals a bus speed of 1066.688, or 1066MHz.

    Here is a partial list of XEON E series processors:
     
    Model Speed (GHz) L3 Cache (MB) QPI speed (GT/s) DDR3 Clock (MHz) TDP (W) Cores Threads Turbo-Boost
    W3680 3.33 12 6.4 1333 130 6 12 Y
    L5609 1.86 12 4.8 1066 40 4 4 N
    L5618 1.86 12 5.86 1066 40 4 8 Y
    L5630 2.13 12 5.86 1066 40 4 8 Y
    E5620 2.40 12 5.86 1066 80 4 8 Y
    E5630 2.53 12 5.86 1066 80 4 8 Y
    E5640 2.66 12 5.86 1066 95 4 8 Y
    X5667 3.06 12 6.4 1333 95 4 8 Y
    X5677 3.46 12 6.4 1333 130 4 8 Y
    L5638 2.00 12 5.86 1333 60 6 12 Y
    L5640 2.26 12 5.86 1333 60 6 12 Y
    E5645 2.40 12 5.86 1333 80 6 12 Y
    X5650 2.66 12 6.4 1333 95 6 12 Y
    X5660 2.80 12 6.4 1333 95 6 12 Y
    X5670 2.93 12 6.4 1333 95 6 12 Y
    X5680 3.33 12 6.4 1333 130 6 12 y

    RAM will also affect the bus speed by ranking and amount of RAM. The Precision T5500 uses 1066 MHz and 1333Mhz DDR3 un-buffered or registered ECC SDRAM memory. There are rules for how the memory is placed, but there is also the amount and rank of RAM that can factor bus speed. Even with the E5570 Xeon, if you max out the using quad ranked RAM in risers, the bus speed is most likely going to drop.

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Affected Products

Fixed Workstations
Article Properties
Article Number: 000178876
Article Type: Solution
Last Modified: 21 Feb 2021
Version:  4
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