QEMU does not require administrative rights to run unless additional kernel modules for improving speed (like KQEMU) are used or certain modes of its network connectivity model are utilized. Simulating multiple CPUs running SMP is possible. It can also use an emulated serial line, without any screen, with applicable operating systems. Instead, it can allow one to access the screen of the guest OS via an integrated VNC server. QEMU does not depend on the presence of graphical output methods on the host system. It can also boot Linux kernels without a bootloader. QEMU integrates several services to allow the host and guest systems to communicate for example, an integrated SMB server and network-port redirection (to allow incoming connections to the virtual machine). Network connectivity can also be achieved by bridging a TUN/TAP interface used by QEMU with a non-virtual Ethernet interface on the host OS using the host OS's bridging features. The virtual network cards can also connect to network cards of other instances of QEMU or to local TAP interfaces.
QEMU can emulate network cards (of different models) which share the host system's connectivity by doing network address translation, effectively allowing the guest to use the same network as the host.
Should the guest system become unusable (through virus attack, accidental system destruction, etc.), the user can delete the overlay and use an earlier emulated disk image. For example, a base image could hold a fresh install of an operating system that is known to work, and the overlay images are used. This provides the possibility for reverting the emulated disk's contents to an earlier state. The QCOW2 format also allows the creation of overlay images that record the difference from another (unmodified) base image file. This way, an emulated 120 GB disk may occupy only a few hundred megabytes on the host. Virtual disk images can be stored in a special format ( qcow or qcow2) that only takes up as much disk space as the guest OS actually uses. USB devices can be completely emulated, or the host's USB devices can be used, although this requires administrator privileges and does not work with some devices. The virtual machine can interface with many types of physical host hardware, including the user's hard disks, CD-ROM drives, network cards, audio interfaces, and USB devices. QEMU supports the emulation of various architectures, including x86, MIPS64 (up to Release 6), SPARC (sun4m and sun4u), ARM (Integrator/CP and Versatile/PB), SuperH, PowerPC ( PReP and Power Macintosh), ETRAX CRIS, MicroBlaze, and RISC-V. Guest operating systems do not need patching in order to run inside QEMU. QEMU can save and restore the state of the virtual machine with all programs running. The most common is Linux's KVM but the project supports a number of hypervisors including Xen, Apple's HVF, Windows' WHPX and NetBSD's nvmm. Hypervisor Support In this mode QEMU either acts as a Virtual Machine Manager (VMM) or as a device emulation back-end for virtual machines running under a hypervisor. QEMU can boot many guest operating systems, including Linux, Solaris, Microsoft Windows, DOS, and BSD it supports emulating several instruction sets, including x86, MIPS, 32-bit ARMv7, ARMv8, PowerPC, RISC-V, SPARC, ETRAX CRIS and MicroBlaze. It can be used to provide virtual hosting of several virtual computers on a single computer. System emulation In this mode QEMU emulates a full computer system, including peripherals. Fast cross-compilation and cross-debugging are the main targets for user-mode emulation. System calls are thunked for endianness and for 32/64 bit mismatches. QEMU has multiple operating modes: User-mode emulation In this mode QEMU runs single Linux or Darwin/ macOS programs that were compiled for a different instruction set. Various parts are released under the BSD license, GNU Lesser General Public License (LGPL) or other GPL-compatible licenses. QEMU was written by Fabrice Bellard and is free software, mainly licensed under the GNU General Public License (GPL for short).
QEMU supports the emulation of various architectures, including x86, ARM, PowerPC, RISC-V, and others. QEMU can also do emulation for user-level processes, allowing applications compiled for one architecture to run on another. It can interoperate with Kernel-based Virtual Machine (KVM) to run virtual machines at near-native speed. It emulates a computer's processor through dynamic binary translation and provides a set of different hardware and device models for the machine, enabling it to run a variety of guest operating systems. QEMU (Quick Emulator ) is a free and open-source emulator.
Linux, Microsoft Windows, macOS and some other UNIX platforms