3.5. System Settings

The System category groups various settings that are related to the basic hardware that is presented to the virtual machine.

Note

As the activation mechanism of Microsoft Windows is sensitive to hardware changes, if you are changing hardware settings for a Windows guest, some of these changes may trigger a request for another activation with Microsoft.

The following tabs are available.

3.5.1. Motherboard Tab

On the Motherboard tab, you can configure virtual hardware that would normally be on the motherboard of a real computer.

  • Base Memory: Sets the amount of RAM that is allocated and given to the VM when it is running. The specified amount of memory will be requested from the host OS, so it must be available or made available as free memory on the host when attempting to start the VM and will not be available to the host while the VM is running. This is the same setting that was specified in the New Virtual Machine wizard, as described in Section 1.8, “Creating Your First Virtual Machine”.

    Generally, it is possible to change the memory size after installing the guest OS. But you must not reduce the memory to an amount where the OS would no longer boot.

  • Boot Order: Determines the order in which the guest OS will attempt to boot from the various virtual boot devices. Analogous to a real PC's BIOS setting, Oracle VM VirtualBox can tell a guest OS to start from the virtual floppy, the virtual CD/DVD drive, the virtual hard drive (each of these as defined by the other VM settings), the network, or none of these.

    If you select Network, the VM will attempt to boot from a network using the PXE mechanism. This needs to be configured in detail on the command line. See Section 7.8, “VBoxManage modifyvm”.

  • Chipset: You can select which chipset will be presented to the virtual machine. In legacy versions of Oracle VM VirtualBox, PIIX3 was the only available option. For modern guest OSes such as Mac OS X, that old chipset is no longer well supported. As a result, Oracle VM VirtualBox supports an emulation of the more modern ICH9 chipset, which supports PCI express, three PCI buses, PCI-to-PCI bridges and Message Signaled Interrupts (MSI). This enables modern OSes to address more PCI devices and no longer requires IRQ sharing. Using the ICH9 chipset it is also possible to configure up to 36 network cards, up to 8 network adapters with PIIX3. Note that the ICH9 support is experimental and not recommended for guest OSes which do not require it.

  • Pointing Device: The default virtual pointing devices for older guests is the traditional PS/2 mouse. If set to USB tablet, Oracle VM VirtualBox reports to the virtual machine that a USB tablet device is present and communicates mouse events to the virtual machine through this device. The third setting is a USB Multi-Touch Tablet which is suited for recent Windows guests.

    Using the virtual USB tablet has the advantage that movements are reported in absolute coordinates, instead of as relative position changes. This enables Oracle VM VirtualBox to translate mouse events over the VM window into tablet events without having to "capture" the mouse in the guest as described in Section 1.9.2, “Capturing and Releasing Keyboard and Mouse”. This makes using the VM less tedious even if Guest Additions are not installed.

  • Enable I/O APIC: Advanced Programmable Interrupt Controllers (APICs) are a newer x86 hardware feature that have replaced old-style Programmable Interrupt Controllers (PICs) in recent years. With an I/O APIC, OSes 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 OSes, 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 OSes 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 OSes 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.

  • Enable EFI: Enables Extensible Firmware Interface (EFI), which replaces the legacy BIOS and may be useful for certain advanced use cases. See Section 3.14, “Alternative Firmware (EFI)”.

  • Hardware Clock in UTC Time: If selected, Oracle VM VirtualBox will report the system time in UTC format to the guest instead of the local (host) time. This affects how the virtual real-time clock (RTC) operates and may be useful for UNIX-like guest OSes, which typically expect the hardware clock to be set to UTC.

In addition, you can turn off the Advanced Configuration and Power Interface (ACPI) which Oracle VM VirtualBox presents to the guest OS by default.

ACPI is the current industry standard to allow OSes 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 Oracle VM VirtualBox. ACPI can only be turned off using the command line. See Section 7.8, “VBoxManage modifyvm”.

Warning

All Windows OSes starting with Windows 2000 install different kernels, depending on whether ACPI is available. This means that ACPI must not be turned off after installation of a Windows guest OS. However, turning it on after installation will have no effect.

3.5.2. Processor Tab

On the Processor tab, you can configure settings for the CPU used by the virtual machine.

  • Processor(s): Sets the number of virtual CPU cores the guest OSes can see. Oracle VM VirtualBox supports symmetrical multiprocessing (SMP) and can present up to 32 virtual CPU cores to each virtual machine.

    You should not configure virtual machines to use more CPU cores than are available physically. This includes real cores, with no hyperthreads.

  • Execution Cap: Configures the CPU execution cap. This limits the amount of time a host CPU spends to emulate a virtual CPU. The default setting is 100%, meaning that there is no limitation. A setting of 50% implies a single virtual CPU can use up to 50% of a single host CPU. Note that limiting the execution time of the virtual CPUs may cause guest timing problems.

    A warning is displayed at the bottom of the Processor tab if an Execution Cap setting is made that may affect system performance.

  • Enable PAE/NX: Determines whether the PAE and NX capabilities of the host CPU will be exposed to the virtual machine.

    PAE stands for Physical Address Extension. Normally, if enabled and supported by the OS, then even a 32-bit x86 CPU can access more than 4 GB of RAM. This is made possible by adding another 4 bits to memory addresses, so that with 36 bits, up to 64 GB can be addressed. Some OSes, such as Ubuntu Server, require PAE support from the CPU and cannot be run in a virtual machine without it.

  • Enable Nested VT-x/AMD-V: Enables nested virtualization, with passthrough of hardware virtualization functions to the guest VM.

    This feature is available on host systems that use an AMD CPU. For Intel CPUs, the option is grayed out.

With virtual machines running modern server OSes, Oracle VM VirtualBox also supports CPU hot-plugging. For details, see CPU Hot-Plugging.

3.5.3. Acceleration Tab

On this tab, you can configure Oracle VM VirtualBox to use hardware virtualization extensions that your host CPU supports.

  • Paravirtualization Interface: Oracle VM VirtualBox provides paravirtualization interfaces to improve time-keeping accuracy and performance of guest OSes. The options available are documented under the paravirtprovider option in Section 7.8, “VBoxManage modifyvm”. For further details on the paravirtualization providers, see Paravirtualization Providers.

  • Hardware Virtualization: You can select for each virtual machine individually whether Oracle VM VirtualBox should use software or hardware virtualization.

    • Enable VT-x/AMD-V: Enables Intel VT-x and AMD-V hardware extensions if the host CPU supports them.

    • Enable Nested Paging: If the host CPU supports the nested paging (AMD-V) or EPT (Intel VT-x) features, then you can expect a significant performance increase by enabling nested paging in addition to hardware virtualization. For technical details, see Nested Paging and VPIDs. For Intel EPT security recommendations, see CVE-2018-3646.

    Advanced users may be interested in technical details about software versus hardware virtualization. See Hardware vs. Software Virtualization.

In most cases, the default settings on the Acceleration tab will work well. Oracle VM VirtualBox selects sensible defaults, depending on the OS that you selected when you created the virtual machine. In certain situations, however, you may want to change the preconfigured defaults.