KVM vs Qemu: What are the differences?

Key Differences between KVM and Qemu

KVM and Qemu are both virtualization technologies that allow for the creation and management of virtual machines. However, there are several key differences between the two:

1. Architecture: KVM, which stands for Kernel-based Virtual Machine, is a Linux kernel module that provides hardware-assisted virtualization. It leverages the processor's virtualization extensions, such as Intel VT-x or AMD-V, to directly run virtual machines. On the other hand, Qemu, which stands for Quick Emulator, is a generic and open-source machine emulator and virtualizer that can be run on a wide range of host operating systems. It emulates the entire hardware environment for virtual machines, without relying on hardware virtualization extensions.

2. Performance: Due to its direct integration with the host kernel and utilization of hardware virtualization extensions, KVM generally provides better performance compared to Qemu. KVM allows for near-native performance, as virtual machines can directly access the underlying hardware. Qemu, being a full-system emulator, relies on software-based emulation, which introduces some overhead and may result in slower performance.

3. Guest support: KVM is specifically designed for hosting virtual machines running Linux as the guest operating system. It provides excellent support for Linux-based virtual machines, allowing them to fully utilize the host's resources and capabilities. Qemu, on the other hand, offers broader guest OS support. It can run virtual machines with various operating systems, including Linux, Windows, macOS, and more.

4. Device emulation: Qemu has extensive device emulation capabilities, allowing it to emulate a wide range of hardware devices. This enables virtual machines running on Qemu to interact with virtualized hardware components, such as network interfaces, storage devices, and USB controllers. While KVM can pass through certain host devices to virtual machines, it does not have the same level of device emulation as Qemu.

5. Management interfaces: KVM is primarily managed through command-line tools and APIs, such as virsh and libvirt. It provides a robust and flexible management interface for virtual machine administration. Qemu also supports command-line management, but it additionally provides graphical user interface (GUI) options, making it more accessible for users who prefer visual administration tools.

6. Integration with other virtualization software: KVM is commonly used in conjunction with additional software, such as the open-source hypervisor, Qemu, to create a complete virtualization stack. KVM provides the virtualization capability, while Qemu handles the machine emulation. In contrast, Qemu can be used as a standalone virtualization solution without KVM, although it may not achieve the same level of performance.

In Summary, KVM is a Linux kernel module that provides hardware-assisted virtualization, while Qemu is a generic machine emulator and virtualizer. KVM offers better performance, excellent Linux guest OS support, and strong command-line management. Qemu, on the other hand, provides broader guest OS support, extensive device emulation capabilities, graphical management options, and can be used independently.