Disk Image Format (.dmg) – Read-only Bochs – Read-only Linux cloop – Read-only Parallels disk image (.hdd, .hds) – Read-only QEMU copy-on-write (.qcow2, .qed, .qcow, .cow) VirtualBox Virtual Disk Image (.vdi) Virtual PC Virtual Hard Disk (.vhd) Virtual VFAT VMware Virtual Machine Disk (.vmdk) Raw images (.img) that contain sector-by-sector contents of a disk CD/DVD images (.iso) that contain sector-by-sector contents of an optical disk (e.g. booting live OSes) QEMU Object Model The QEMU Object Model (QOM) provides a framework for registering user creatable types and instantiating objects from those types. QOM provides the following features: System for dynamically registering types Support for single-inheritance of types Multiple inheritance of stateless interfaces Hardware-assisted emulation The MIPS-compatible Loongson-3 processor adds 200 new instructions to help QEMU translate x86 instructions; those new instructions lower the overhead of executing x86/CISC-style instructions in the MIPS pipeline. With additional improvements in QEMU by the Chinese Academy of Sciences, Loongson-3 achieves an average of 70% the performance of executing native binaries while running x86 binaries from nine benchmarks. , no source code has been published for this fork, so the claim cannot be verified independently. Parallel emulation Virtualization solutions that use QEMU are able to execute multiple virtual CPUs in parallel. For user-mode emulation QEMU maps emulated threads to host threads. For full system emulation, QEMU is capable of running a host thread for each emulated virtual CPU (vCPU). This is dependent on the guest having been updated to support parallel system emulation, currently ARM, Alpha, HP-PA, PowerPC, RISC-V, s390x, x86 and Xtensa. Otherwise a single thread is used to emulate all virtual CPUS (vCPUS) which executes each vCPU in a round-robin manner. Integration VirtualBox VirtualBox, first released in January 2007, used some of QEMU's virtual hardware devices, and had a built-in dynamic recompiler based on QEMU. As with KQEMU, VirtualBox runs nearly all guest code natively on the host via the VMM (Virtual Machine Manager) and uses the recompiler only as a fallback mechanism - for example, when guest code executes in real mode. In addition, VirtualBox did a lot of code analysis and patching using a built-in disassembler in order to minimize recompilation. VirtualBox is free and open-source (available under GPL), except for certain features. Xen-HVM Xen, a virtual machine monitor, can run in HVM (hardware virtual machine) mode, using Intel VT-x or AMD-V hardware x86 virtualization extensions and ARM Cortex-A7 and Cortex-A15 virtualization extension.