APIC switch-off without reinstalling Windows

PC/104 to CAN Interface
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APIC switch-off without reinstalling Windows

Post by M.Gerber » Thu 16. Feb 2012, 15:49


The PCAN-PC/104 card (as well as the PCAN-ISA card) must be run in a computer with APIC mode disabled. If you need to change this low-level setting in the BIOS setup, usually Windows cannot restart afterwards - a reinstallation or a repair installation of the OS is necessary.

Fortunately, this can be circumvented by installing the necessary driver in Windows before switching off the APIC mode in the BIOS setup. :idea:

NOTE 1: APIC is essential for using multiple processors/cores in a system. If you disable APIC, only a single processor/core is detected and used by Windows in a multi-processor system afterwards.

NOTE 2: The following procedure is one-way. You cannot go back the easy way. If you want to reactivate APIC later on for any reason, you must reinstall Windows (or try a repair installation).

:arrow: Do the following in order to deactivate APIC:
  1. In Windows, start the Device Manager.
  2. Open the Computer branch and select the ACPI Uniprocessor PC entry.
    On multi-processor systems the marked entry is shown as "ACPI Multiprocessor PC"
    On multi-processor systems the marked entry is shown as "ACPI Multiprocessor PC"
    DeviceManager_Computer.png (20.88 KiB) Viewed 6910 times
  3. Click on the Update Driver icon as shown above (can be done also via context menu).
    The Hardware Update Wizard pops up.
  4. Follow the steps of the Wizard by checking those options that are related to a manual installation of a driver (usually the lower entries of the option lists).
  5. When you get to the driver list, select the Advanced Configuration and Power Interface (ACPI) PC entry as shown below and click on Next.
    SelectDeviceDriver.png (18.53 KiB) Viewed 6910 times
    Windows installs the needed files and requests a reboot.
  6. Confirm the reboot request and (!) enter the BIOS setup when the PC restarts.
  7. Disable the APIC mode in the BIOS setup, save the changes, and quit the BIOS setup.
  8. After Windows has (hopefully) restarted flawlessly and after some further seconds Windows asks for a second reboot. Confirm this and after another boot cycle you're done. :)
This procedure does not apply to all computers. For example, very old hardware doesn't even have an APIC mode, so you would search there for nothing. Also, this procedure isn't exhaustedly tested for
all kind of hardware. See it as a tip for saving some effort and time.

If not sure, you're welcome to ask here.


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