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<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE topic PUBLIC "-//OASIS//DTD DITA Topic//EN" "topic.dtd">
<topic xml:lang="en-us" id="settings-processor">
<title>Processor Tab</title>
<body>
<p>On the <b outputclass="bold">Processor</b> tab, you can configure settings for the CPU used by the virtual
machine. </p>
<ul>
<li>
<p><b outputclass="bold">Processor(s):</b> Sets the
number of virtual CPU cores the guest OSes can see.
<ph conkeyref="vbox-conkeyref-phrases/product-name"/> supports symmetrical multiprocessing (SMP)
and can present up to 32 virtual CPU cores to each virtual
machine.
</p>
<p>
You should not configure virtual machines to use more CPU
cores than are available physically. This includes real
cores, with no hyperthreads.
</p>
</li>
<li>
<p><b outputclass="bold">Execution Cap:</b> 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.
</p>
<p>
A warning is displayed at the bottom of the Processor tab if
an Execution Cap setting is made that may affect system
performance.
</p>
</li>
<li>
<p><b outputclass="bold">Enable PAE/NX (Can't be changed on VMs with an Arm architecture):</b> Determines whether the PAE and NX capabilities of the host CPU will be exposed to the virtual machine. </p>
<p>
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.
</p>
</li>
<li>
<p><b outputclass="bold">Enable Nested VT-x/AMD-V (Can't be changed on VMs with an Arm architecture)</b>: Enables nested virtualization, with passthrough of hardware virtualization functions to the guest VM. </p>
</li>
</ul>
<p>With virtual machines running modern server OSes, <ph conkeyref="vbox-conkeyref-phrases/product-name"/> also
supports CPU hot-plugging. For details, see <xref href="cpuhotplug.dita">CPU Hot-Plugging</xref>. </p>
</body>
</topic>
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