ACPI vs APM ???

By RustyZip
Oct 22, 2002
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  1. With all these threads about power management, ACPI, APM etc etc, i wondered which is best - ACPI or APM. And why?

    At the mo, i've got ACPI disabled in BIOS and APM enabled in WIN XP and everythings fine (and shuts down ok) etc,

    But which is best and why ????
  2. Rick

    Rick TechSpot Staff Posts: 6,304   +52 Staff Member

    ACPI is newer and more cross-platform than APM from what I understand. So obviously APM is better suited for older systems than newer ones, since older systems usually don't properly support ACPI. Here's a list of pros and cons I can think of

    APM cons:

    APM is messy and less standardized, depending more on BIOSes than the Operating System. Since each BIOS varies, it can cause some strange, random problems system to system such as stanby crashing your system or certain devices no being compatible with your setup. The BIOS also doesn't have a clue what in the heck you are doing while you are using your computer, so powermangement can't be as "smart" as it is in ACPI.

    APM Pros:

    I suppose legacy support is the big thing here. Older devices should be properly supported and older computers should just work better with APM enabled. APM gives the power user control over IRQs through the BIOS, so if you are having conflicts, it is generally easy to get around them. ACPI controls much of this information. In some instances, APM has proven to be faster than ACPI because ACPI shares so many devices on one IRQ at times.



    ACPI cons:

    It's new, so many older devices not designed for ACPI will not work properly or at all. Those older devices that do function, usually don't support advanced ACPI features such as "sleeping".
    ACPI's agressive IRQ sharing can cause your system to run more slowly than it should sometimes, but usually allows you to avoid IRQ conflicts as a whole. Also, putting your Operating System in total control of your computer can have some unexpected results such as unexplained power failures or freaky behavior.

    ACPI pros:

    It's the new open standard, supported by almost any modern OS. Devices and motherboards are now specifically designed for ACPI compliancy, which makes this probably the most compatible for hardware in the last few years. ACPI generally avoids IRQ conflicts where APM would have them by sharing IRQs. You also get advanced power management, allowing certain devices to "sleep", saving power. It's great for laptops and the life of your computer in general, I would imagine.


    Personally, I have ACPI disabled.. Not because I don't like it, because my video card has some issues with it. If you can, I would recommend using it.
  3. StormBringer

    StormBringer Newcomer, in training Posts: 2,871

    I also have it disabled because my capture card has issues with it. Seems there may have been something else that didn't get along too well with it as well. I used to recommend disabling it, but if all your hardware will work fine with it enabled then keep it, if not kill it.
  4. RustyZip

    RustyZip TechSpot Paladin Topic Starter Posts: 415

    Thanks for replies guys...

    So i suppose as everythings running ok, i'll leave ACPI disabled and use APM...

    Just a thought: Is one quicker than the other, and which if either uses less resources??
  5. Rick

    Rick TechSpot Staff Posts: 6,304   +52 Staff Member

  6. Mictlantecuhtli

    Mictlantecuhtli TechSpot Evangelist Posts: 4,916   +9

    Probably the biggest difference between ACPI and APM is that APM is only power management while ACPI is system-wide, handles IRQs, device initializations as well as power management, among other things.
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