I set 2 CPU on virtualbox xp and boot successfully.

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But when I use speccy to check.

It says I only have 1 cpu and only 1 core.

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What happened?

How do I enable the second CPU?

Thank you~

  • Did you enable VT-x in BIOS?
    – Takkat
    Dec 20 '11 at 7:48
  • Did you enable I/O APIC for the VM before installing Windows?
    – Takkat
    Dec 20 '11 at 8:06
  • Yes,I have enabled VT-x in BIOS. But I do not enable I/O APIC before installing windows. How to fix it? Thank you~
    – sam
    Dec 20 '11 at 9:16
  • may be as an old operating system(Win XP) it wouldn't support 2 CPU in hardware Dec 20 '11 at 12:35
  • Here is solution (use devcon utility and execute two commands) - superuser.com/a/456617
    – Eugene R.
    Jan 19 '13 at 10:54

For Windows 64-bit guest and if you want to use more than 1 CPU in your guest we need to enable I/O APIC prior to installing Windows.

Enabling the I/O APIC is required for 64-bit guest operating systems, especially Windows Vista; it is also required if you want to use more than one virtual CPU in a virtual machine.

Reference: Virtual Box User Manual

This can be done in the System -> Motherboard setting in the VirtualBox Manager.

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Note: These setting has to be made before installing Windows as only then Windows will be installed with the appropriate kernel.

  • I use 32-bit XP. And I also have already enabled IO APIC. What can I do next? Thank you~
    – sam
    Dec 20 '11 at 10:20
  • @sam: as said, you may need to reinstall XP with these settings.
    – Takkat
    Dec 20 '11 at 10:25
  • I can't reinstall xp because some software problems. Is there any other way to get this function without reinstall?
    – sam
    Dec 20 '11 at 13:49
  • I don't know if you can change the Windows kernel without fresh install (may well be you can't). Consider asking this on superuser.com
    – Takkat
    Dec 20 '11 at 13:56
  • According to this blog post you can simply run the following in a command prompt within the windows guest: rundll32 syssetup,SetupInfObjectInstallAction ACPIAPIC_MP_HAL 128 %windir%\inf\hal.inf and then reboot twice as prompted.
    – davitenio
    Dec 13 '13 at 7:43
  1. Click the "Enable IO APIC" checkbox in the System settings of your virtual box guest machine.
  2. Run the following in a command prompt inside the windows guest:

rundll32 syssetup,SetupInfObjectInstallAction ACPIAPIC_MP_HAL 128 %windir%\inf\hal.inf

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