What is SMI pins on the MOBO panel?

Discussion in 'Asus' started by Go Tyler, Dec 15, 2005.

  1. Go Tyler

    Go Tyler Guest

    I found it.

    As a quick introduction, SMIs were introduced to the x86 world by the 386SL.
    It was created to allowed systems designers to have access to the CPU while
    unspecified software of any type was running. The reasons for this are
    obvious when you look at the market the 386SL was aimed it. It was Intel's
    first attempt at a truly mobile CPU. SMIs allowed the BIOS to control
    various aspects of power management on the CPU, regardless of what kind of
    OS was running on top of it. That was a good thing in the days when DOS
    still ruled the land. DOS knew as much about power management as your
    average light bulb, and letting the system designer control how and when
    devices were turned on and off seemed like a great solution. The problem is
    how it was implemented

    To implement SMI, Intel created a new interrupt pin on their CPU,
    appropriately named the SMI# pin. When this pin was asserted, (turned on,
    essentially) the system would halt everything it was doing, save state, and
    transition into System Management Mode (SMM). SMM is essentially another
    entire operating mode for the CPU, just like Real Mode, V86 Mode, and
    Protected Mode. The big difference here is that this mode can't be signaled
    from software, and everything that happens is 100% transparent to software.
    Once the system enters into SMM mode, it's truly like time stands still.
    Everything you know about the state of the system can change from underneath
    you from one instruction to the next. This includes every part of the OS,
    which generally assumes, (rightfully so) that things will always be a
    certain way until it says otherwise.

    ----- Original Message -----
    From: "Go Tyler" <>
    Newsgroups: alt.comp.periphs.mainboard.asus
    Sent: Wednesday, December 14, 2005 7:34 PM
    Subject: What is SMI pins on the MOBO panel?
    Go Tyler, Dec 15, 2005
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