2 "processor" tab, Processor” tab, 2 “processor” tab – Sun Microsystems VIRTUALBOX VERSION 3.1.0_BETA2 User Manual
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3 Configuring virtual machines
Enable I/O APIC
Advanced Programmable Interrupt Controllers (APICs) are a newer
x86 hardware feature that have replaced old-style Programmable Interrupt Con-
trollers (PICs) in recent years. With an I/O APIC, operating systems can use more
than 16 interrupt requests (IRQs) and therefore avoid IRQ sharing for improved
reliability.
Note: 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.
However, software support for I/O APICs has been unreliable with some operat-
ing systems other than Windows. Also, the use of an I/O APIC slightly increases
the overhead of virtualization and therefore slows down the guest OS a little.
Warning: All Windows operating systems starting with Windows 2000 install
different kernels depending on whether an I/O APIC is available. As with
ACPI, the I/O APIC therefore must not be turned off after installation of a
Windows guest OS. Turning it on after installation will have no effect however.
In addition, you can turn off the Advanced Configuration and Power Interface
(ACPI) which VirtualBox presents to the guest operating system by default. ACPI is the
current industry standard to allow operating systems to recognize hardware, configure
motherboards and other devices and manage power. As all modern PCs contain this
feature and Windows and Linux have been supporting it for years, it is also enabled
by default in VirtualBox. It can be turned off on the command line; e see chapter
, page
Warning: All Windows operating systems starting with Windows 2000 install
different kernels depending on whether ACPI is available, so ACPI must not
be turned off
after installation of a Windows guest OS. Turning it on after
installation will have no effect however.
3.4.2 “Processor” tab
On the “Processor” tab, you can set how many virtual CPU cores the guest operating
systems should see. Starting with version 3.0, VirtualBox supports symmetrical multi-
processing (SMP) and can present up to 32 virtual CPU cores to each virtual machine.
You should not, however, configure virtual machines to use more CPU cores than
you have available physically.
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