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ManualsBrandsRed Hat ManualsComputer equipmentENTERPRISE LINUX 5 - VIRTUALIZATION GUIDE
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Virtualized and emulated devices
3
• Emulated software devices.
• Para-virtualized devices.
• Physically shared devices.
These hardware devices all appear as physically attached hardware devices to the virtualized guest
but the device drivers work in different ways.
1.4.1. Virtualized and emulated devices
The KVM hypervisor implements many core devices for virtualized guests in software. These emulated
hardware devices are crucial for virtualizing operating systems. This section is provided as an
introduction to the emulated devices and emulated device drivers.
Emulated devices are virtual devices which exist entirely in software. The emulated devices do not
require a real hardware device to back them.
Emulated drivers may use either a physical device or a virtual software device. Emulated drivers are
a translation layer between the guest and the Linux kernel (which manages the source device). The
device level instructions are completely translated by the KVM hypervisor. Any device, of the same
type, recognized by the Linux kernel may be used as the backing source device for the emulated
drivers.
Virtualized CPUs (VCPUs)
A system has a number of virtual CPUs (VCPUs) relative to the number of physical processor cores.
The number of virtual CPUs is finite and represents the total number of virtual CPUs that can be
assigned to guest virtual machines.
Emulated graphics devices
Two emulated graphics devices are provided. These devices can be connected to with the SPICE
protocol or with VNC.
• The ac97 device emulates a Cirrus CLGD 5446 PCI VGA card.
• The vga device emulates a dummy VGA card with Bochs VESA extensions (hardware level,
including all non-standard modes).
Emulated system components
Various core system components are emulated to provide basic system functions.
• A Cirrus i440FX host PCI bridge.
• PIIX3 PCI to ISA bridge.
• A PS/2 mouse and keyboard.
• An EvTouch USB Graphics Tablet.
• A PCI UHCI USB controller and a virtualized USB hub.
• A PCI and ISA network adapters.
• Emulated serial ports.