What's the deal with variable bus timing?

Discussion in 'Macintosh Computers' started by Boomer Mac, Nov 5, 2002.

  1. macrumors newbie

    What's the deal with variable bus timing?

    I could be wrong here but maybe some of the techies
    can correct me:

    Isn't variable bus timing the same (or similar) to
    speedstep technology on the higher end Pentium mobile

    Speedstep technology determines what you are running (in terms
    of active applications) at a given point in time and adjusts
    the computing cycles so the processor draws less power when running relatively non-power hungry programs and therefor
    battery life is prolonged.

    How is this different from variable bus timing as it has been explained in preview articles?

    Please give me some insight.

    Boomer Mac
  2. macrumors 601


    I am certainly no expert on the subject, but its possible its just two different technologies to accomplish a similar goal.
  3. macrumors 604


    Will this cause a speed decrease?
  4. macrumors newbie

    To my knowledge, no speed decreases were noted
    on Pentium Mobile equipped notebooks.
  5. macrumors 604


    Is there variable bus timing in the new powerbooks?
  6. macrumors member

    Speedstep just slows down the processor. For example, if your processor was nomaly running at 1Ghz and your bus was at 133. If your processor would drop down to something like 733mhz due to speedstep your bus speed would stay at 133.

    Variable bus timing would slow down the processor and the sysetm bus. So if you were running at 1ghz on a 133mhz bus, you might drop down to some thing like 750mhz on a 100mhz bus.

    Considering logic chips are getting hot enough to require their own heatsinks or fans, variable bus timing might be a good thing.
  7. macrumors 604


    Disregard that post. I just figured out that the powerbooks do not have variable bus timing. So if anyone else was wondering if the powerbooks had this technology, the answer is no. Thanks to Over Achiever for this information.
  8. Moderator emeritus


    Really? What is this in the Energy Saver pref pane for? ;)

    Attached Files:

  9. macrumors 604


    CPU speed stepping.
  10. Moderator emeritus


    Meaning when the CPU is not active it will idle to save on battery power. In other words, downclocking, i.e. 500MHz down to 400MHz.

    Isn't that variable timing? The timing (clockspeed) is variable (changes). Isn't this just semantics?

    Why differentiate whether just the CPU clock changes or if the clock and FSB changes?
  11. macrumors 604


    Because the CPU and the FSB are two separate chips.

    The variable bus timing slows the bus down and the cpu down. The cpu stepping just slows the cpu down.
  12. Moderator emeritus


    Actually, the FSB is not a "chip", but the connection between the CPU and the rest of the system components and determines the speed of the system overall.

    Anyway, why differentiate between the two (speed stepping and variable timing) if they both accomplish the same thing?
  13. macrumors 604


    I meant to say system bus not fsb.

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