In virtualization, emulated devices are virtual representations of hardware devices. Instead of providing direct access to the physical hardware, the hypervisor or virtual machine monitor provides an emulated version of a device that virtual machines can interact with. This emulation enables virtual machines to operate as though they are communicating with real hardware, even though they are really interacting with a software-based representation of that hardware.

Here are some key points about emulated devices:

  1. Compatibility: Emulated devices mimic well-known hardware, ensuring that most operating systems include drivers for these devices out of the box.
  2. Isolation: Since emulated devices don’t provide direct access to the underlying hardware, they can offer an additional layer of isolation between the virtual machine and the physical host, potentially improving security.
  3. Performance Overhead: Emulation generally involves translating the virtual machine’s operations into operations that the physical hardware can understand. This translation process can introduce some performance overhead, making emulated devices typically slower than paravirtualized or hardware-assisted devices.
  4. Common Emulated Devices: Commonly emulated devices in virtualized environments include graphics adapters, network cards, disk controllers, USB controllers, and more. For instance, VMware might present an emulated Intel E1000 network adapter to the virtual machine, while QEMU/KVM might offer an emulated Realtek RTL8139 network card.
  5. Use Cases: Emulated devices are particularly useful when running older operating systems that might not support modern hardware or when ensuring compatibility across various virtualization platforms.
  6. Paravirtualization vs. Emulation: In contrast to emulation, paravirtualization involves modifying the guest operating system to be aware of the virtualized environment. Paravirtualized devices often offer better performance than emulated devices but require guest OS support.

In summary, emulated devices play a crucial role in virtualization, offering compatibility and isolation at the expense of some performance overhead. They allow virtual machines to function on a wide variety of hardware without requiring direct access to the physical devices.