| 1 | <?xml version='1.0' encoding='UTF-8'?>
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| 2 | <!DOCTYPE topic PUBLIC "-//OASIS//DTD DITA Topic//EN" "topic.dtd">
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| 3 | <topic xml:lang="en-us" id="settings-processor">
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| 4 | <title>Processor Tab</title>
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| 5 |
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| 6 | <body>
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| 7 | <p>On the <b outputclass="bold">Processor</b> tab, you can configure settings for the CPU used by the virtual
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| 8 | machine. </p>
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| 9 | <ul>
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| 10 | <li>
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| 11 | <p><b outputclass="bold">Processor(s):</b> Sets the
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| 12 | number of virtual CPU cores the guest OSes can see.
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| 13 | <ph conkeyref="vbox-conkeyref-phrases/product-name"/> supports symmetrical multiprocessing (SMP)
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| 14 | and can present up to 32 virtual CPU cores to each virtual
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| 15 | machine.
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| 16 | </p>
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| 17 | <p>
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| 18 | You should not configure virtual machines to use more CPU
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| 19 | cores than are available physically. This includes real
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| 20 | cores, with no hyperthreads.
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| 21 | </p>
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| 22 | </li>
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| 23 | <li>
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| 24 | <p><b outputclass="bold">Execution Cap:</b> Configures
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| 25 | the CPU execution cap. This limits the amount of time a host
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| 26 | CPU spends to emulate a virtual CPU. The default setting is
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| 27 | 100%, meaning that there is no limitation. A setting of 50%
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| 28 | implies a single virtual CPU can use up to 50% of a single
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| 29 | host CPU. Note that limiting the execution time of the
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| 30 | virtual CPUs may cause guest timing problems.
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| 31 | </p>
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| 32 | <p>
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| 33 | A warning is displayed at the bottom of the Processor tab if
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| 34 | an Execution Cap setting is made that may affect system
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| 35 | performance.
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| 36 | </p>
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| 37 | </li>
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| 38 | <li>
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| 39 | <p><b outputclass="bold">Enable PAE/NX:</b> Determines
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| 40 | whether the PAE and NX capabilities of the host CPU will be
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| 41 | exposed to the virtual machine.
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| 42 | </p>
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| 43 | <p>
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| 44 | PAE stands for Physical Address Extension. Normally, if
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| 45 | enabled and supported by the OS, then even a 32-bit x86 CPU
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| 46 | can access more than 4 GB of RAM. This is made possible by
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| 47 | adding another 4 bits to memory addresses, so that with 36
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| 48 | bits, up to 64 GB can be addressed. Some OSes, such as
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| 49 | Ubuntu Server, require PAE support from the CPU and cannot
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| 50 | be run in a virtual machine without it.
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| 51 | </p>
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| 52 | </li>
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| 53 | <li>
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| 54 | <p><b outputclass="bold">Enable Nested VT-x/AMD-V</b>:
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| 55 | Enables nested virtualization, with passthrough of hardware
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| 56 | virtualization functions to the guest VM.
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| 57 | </p>
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| 58 | </li>
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| 59 | </ul>
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| 60 | <p>With virtual machines running modern server OSes, <ph conkeyref="vbox-conkeyref-phrases/product-name"/> also
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| 61 | supports CPU hot-plugging. For details, see <xref href="cpuhotplug.dita">CPU Hot-Plugging</xref>. </p>
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| 62 | </body>
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| 63 |
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| 64 | </topic>
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